Methods of preparing a foam comprising a sclerosing agent

ABSTRACT

Present application discloses a device for generating and dispensing a foam for therapeutic use comprising a) a housing, b) a first chamber with gas at a substantially atmospheric pressure, a second chamber with at least one sclerosant agent c) an outlet for dispensing gas and the solution in the form of a foam d) the flow path for mixing the gas and the solution e) a foaming unit.

This application claims priority of U.S. Provisional Application Nos.60/542,867 and 60/542,866 filed, Feb. 10, 2004. The application alsoclaims priority of UK Patent Application Nos. 0422307.9 , filed Oct. 7,2004, and 0326768.9, filed Nov. 17, 2003. All of these applications areherein incorporated by reference.

The present invention relates to the generation of foam comprising asclerosing material, particularly a sclerosing solution, which issuitable for use in the treatment of various medical conditionsinvolving blood vessels, particularly varicose veins and other disordersinvolving venous malformation.

Sclerosis of varicose veins is based on the injection into the veins ofliquid sclerosant substances which, by inter alia causing a localisedinflammatory reaction, favor the elimination of these abnormal veins.Until recently, sclerotherapy was a technique selected in cases of smalland medium caliber varicose veins, those with diameters equal to orgreater than 7 mm being treated by surgery.

An injectable microfoam suitable for therapeutic use, on larger veins inparticular, has now been developed and is described in EP-A-0656203 andU.S. Pat. No. 5676962 (Cabrera & Cabrera), incorporated herein byreference. These describe a low-density microfoam produced with asclerosing substance which, when injected into a vein, displaces bloodand ensures that the sclerosing agent contacts the endothelium of thevessel in a known concentration and for a controllable time, achievingsclerosis of the entire segment occupied.

Prior to the priority date of these patents it had been known for manyyears that injection of liquid sclerosant into varicose veins,especially smaller varicose veins, could be effective. It had also beenknown for many years to inject a small quantity of air into a vein priorto injecting sclerosing liquid, the objective being to displace bloodfrom the vein to avoid the sclerosing agent being diluted too quickly. Adevelopment of this technique was to make a loose foam or froth and toinject this instead of pure air, prior to injection of the sclerosantliquid. These techniques, known as “air block” and developed by Orbach,were generally only effective for treating smaller veins.

In addition there had been disclosures of finer foams for treatment ofsmaller varicose veins (Fluckiger references cited below), or a combinedprocedure using both surgery and foam for treatment of the entire longsaphenous vein: Mayer; Brucke: “The Aetiology and Treatment ofVaricosities of the Lower Extremities”, Chirurgische Praxis, 521-528,1957.

All of these prior disclosures of foam/froth treatment describe thepreparation of the foam/froth with air as the gaseous component. None ofthe documents mentions the air in the injected foam giving rise toserious problems. One reference mentions an apparently short lived airembolism: P. Fluckiger: “Non-surgical retrograde sclerosis of varicoseveins with Varsyl foam”, Schweizerische Medizinische Wochenschrift No.48, pp 1368-1370 (1956). In this article, the author indicates that hereduced the volume of foam administered to 10 ml from 15 ml as a resultof a patient experiencing chest pain on standing immediately aftertreatment with 15 ml of foam. In a later lecture, the same authorindicates that he has in fact subsequently used 15 ml foam withoutnoting ill effects: lecture dated 1962 entitled “A contribution totechniques for outpatient treatment of varicose veins” delivered to theHamburg Dermatological Society. The reference by Mayer and Brucke citedabove appears to describe the use of as much as 50 ml of air foam anddoes not mention any problems.

However, it is known that rapid intravenous injection of a largequantity of air, as opposed to air foam, can lead to air embolism whichmay be fatal. In spite of this practitioners of the air block and foamtechniques described above do not report that the volumes of airinvolved in their techniques were sufficient to cause serious problems.

The air block technique had largely fallen out of favor by the 1980s andthe other foam techniques mentioned above were virtually unheard-of.

The Cabreras proposed the use of a microfoam, that is to say a microfoamwith microscopically small bubbles, e.g., where the majority of thebubbles are not visible to the naked eye, for injection into varicoseveins. The use of a microfoam, as opposed to larger bubbled foam orfroth, gives rise to many advantages in terms of controllability andability to displace blood in even the largest varicose veins, allowingtreatment of virtually all varicose veins without recourse to surgery.As used here, the term foam encompasses foams with bubbles of all sizesincluding microfoams.

The first teaching that potential issues with intravenous injection of amicrofoam product made with air are serious enough to warrant change isto be found in the Cabrera patent references mentioned above. Thesedocuments indicate that the prior air based techniques are “dangerousowing to the side effects of atmospheric nitrogen which is only slightlysoluble in blood”, though it is not mentioned exactly what the dangersare nor what volumes or rates of injection of air or nitrogen gas giverise to these dangers.

In addition to being the first to propose a microfoam as opposed to alarger bubbled foam, and to propose treatment of even the largest veinswithout surgery, the Cabreras also proposed that the microfoam be madewith oxygen or a mixture of carbon dioxide and oxygen. In the context ofthis background, the Cabreras' contribution can be seen to be highlyinnovative in a number of respects—appreciating against the prevailingthinking at the time (i) the potential of a sclerosant microfoam, (ii)the need for soluble gases, (iii) the use of oxygen which does notdegrade the microfoam yet is taken up by blood, (iv) the safety ofoxygen but also (v) the possibility of incorporating a percentage ofhighly soluble carbon dioxide.

Since publication of the Cabreras' microfoam technique in the mid 1990smany practitioners have adopted foam both in Europe and the USA. At therecent worldwide conference of phlebologists in San Diego in August2003, approximately one third of the two hundred and fifty or so paperswhich were presented concerned foam treatment.

Almost without exception, however, practitioners using sclerosing foamtoday make it with air. Opinion varies as to how much foam should beinjected—some advocate as little as 5 ml whilst others are prepared toinject more.

The Cabreras' microfoam is prepared extemporaneously in the clinicimmediately prior to use. The preparation involves beating sclerosantsolution with a small brush rotated at high speed by a motor, under acover which is connected to a source of oxygen or oxygen and carbondioxide. Most practitioners who have followed the Cabreras use analternative technique for extemporaneous preparation of foam whichinvolves passing sclerosant solution and air repeatedly between twoconnected syringes. Another alternative is a syringe with a secondplunger with holes in its face and which is independently movable in thesyringe barrel to froth a liquid and gas mixture in the syringe. Both ofthese latter types of procedure are somewhat inconvenient and allow forvariation of the foam composition depending upon the person preparingit: gas content, bubble size, density and stability all requireattention. These techniques require a high degree of care and knowledgethat may be difficult to replicate under pressure, i.e. when timeavailable to prepare the foam is short.

A product which aims essentially to reproduce the Cabreras' microfoam ina more convenient and easily reproducible way is currently beingdeveloped and is in clinical trials in Europe and the USA. This productis a pressurized canister system, in which the foam is produced bypassing gas and sclerosant solution under pressure through a number offine meshes. In the trials of this product the aim is to treat an entirelong saphenous vein and its varicosed tributaries in a single treatment,which can mean injection of 25 ml or even 50 ml of foam.

WO 00/72821-A1 (BTG International Limited), incorporated herein byreference, describes the fundamental concepts underlying this canisterproduct. The foam is produced by passing gas and sclerosant liquidthrough one or more meshes having small apertures measured in microns.Like the Cabrera patents, this document acknowledges the potentialissues with air/nitrogen and seeks to reduce the levels of nitrogen inthe foam. A preferred form of gas described in WO 00/72821-A1 comprises50% vol/vol or more oxygen, the remainder being carbon dioxide, orcarbon dioxide, nitrogen and trace gases in the proportion found inatmospheric air.

In a later patent application, WO 02/41872-A1 (BTG InternationalLimited), incorporated herein by reference, the sclerosant liquid and anoxygen-rich physiologically acceptable blood dispersible gas are storedin separate containers until immediately prior to use, when theblood-dispersible gas is introduced into the container holding thesclerosant liquid. The mixture of blood-dispersible gas and sclerosantliquid is then released, the components of the mixture interacting uponrelease of the mixture to form a sclerosing foam. In the systemdescribed in this patent application, a proportion of nitrogen (25%) isdeliberately introduced into the polidocanol canister. After charging ofthe sclerosing liquid (polidocanol) can with oxygen from the higherpressure oxygen canister, the percentage of nitrogen is reduced to about7 or 8%. It was believed that this level of nitrogen could be tolerated.

The device disclosed in WO 02/41872-A1 gives a good uniform injectablefoam, irrespective of the gases used. Use of 100% CO₂ as the filling gasin the polidocanol canister is preferred, as CO₂ is very soluble in thebloodstream, but the present inventors have observed that increasing CO₂percentage in the final gas mix may cause an undesirable decrease infoam stability, resulting in a shorter half separation time. Inparticular, the half-life of the foam can fall short of the figure of2.5 minutes which is indicated in WO 00/72821-A1 as being preferable.

The present inventors are continuing to research clinical aspects of theinjection of sclerosing foam as well as developing the canister foamproduct and putting it through clinical trials in Europe and the USA. Ithas always been the intention to develop a safe foam product which is aswell defined as possible but whose specification has achievabletolerances. There are many parameters of a foam which may be varied.These include, without limitation: the chemical, its purity and thestrength of the solution; the size of bubbles, or more accurately thedistribution of sizes, the density (i.e. ratio of liquid to gas), thelongevity of the foam (measured in terms of “half life”, or the timetaken for half the foam to revert to liquid) and the gas mixture.

Nitrogen, which makes up approximately 80% of air, is difficult as apractical matter to exclude totally from a foam. This is true whetherthe foam is made using a canister system, in which case nitrogen tendsto creep into the canister during manufacture, or using either of thesyringe techniques or the Cabreras' rotating brush technique, or indeedany of a number of other less common techniques which have beendeveloped since the Cabreras' disclosure of microfoam.

In a two syringe technique the likely method for introducing the gascomponent, if a foam were to be made with a gas other then air, would beto connect one syringe to a pressurized source of gas, then disconnectand reconnect it to another syringe containing sclerosant. In this sortof technique, the two syringes are pumped to create foam and then thefoam-filled syringe separated. The potential for ingress of a smallpercentage of air/nitrogen during this process is obvious. Similarly,even with the Cabreras' technique, it may be difficult to exclude 100%of air/nitrogen from the environment in which the foam is prepared.

One of the objectives of the foam product being developed by theinventors is to treat an entire greater saphenous vein together withmajor varicose tributaries in a human patient with one injection. Thisrequires up to 25 ml, 30 ml or possibly even 50 ml of foam. Currently,the most conservative users of air foam inject a maximum of 5 ml intothe venous system, apparently without observing any deleterious effects.The inventors therefore reasoned that an equivalent amount of nitrogenin a relatively large dose of foam needed to treat the entire saphenousvein should also be safe. They therefore used this as a starting point:5 ml of air with 80% nitrogen will contain 4 ml nitrogen; acorresponding proportion of nitrogen in, say, 50 ml of low nitrogen foamwould be around 8%.

Until recently, its has been believed by the inventors that a foam withapproximately 8% nitrogen would be acceptable from a safety standpointand that this percentage represented an easily achievable tolerance fornitrogen levels in the foam specification. Accepting this level ofnitrogen also has the advantage that a small quantity of nitrogen couldbe introduced deliberately into the polidocanol canister to reduce theadverse effects of the highly soluble carbon dioxide on the foamstability (as discussed above). This foam and a system for making it isdescribed in WO 02/41872-A1, referred to above.

As discussed above, apart from the above mentioned patent publications,the published art on foam treatment of varicose veins mentions little ifany danger from injecting air foam up to 15 ml. The only event noted byFluckiger was temporary chest pain. The above mentioned patentpublications which mention dangers with nitrogen are silent regardingthe amount of nitrogen which would be dangerous and what damagingeffects it may cause. A great many practitioners are currently using airbased foam, though some restrict the quantity injected to 5 ml. Theinventors have been involved in a 650 patient multi-center Europeanphase III clinical trial of the canister product described above whichcontains 7-8% nitrogen; no serious adverse events associated with thegas component of the foam were noted.

Now, further research in connection with the clinical trials of thecanister system described above has revealed the presence of largenumbers of bubbles in the heart, some of which endure for a significantperiod of time. Ultrasound monitoring of the heart during treatment ofpatients in this trial has revealed many bubbles on the right side ofthe heart and in associated blood vessels. Since foam is injected intothe venous circulation, i.e. that connected to the right side of theheart, it was expected that some bubbles on the right side of the heartwould be observed. However, the number and persistence of the bubbleswas surprising.

Furthermore, bubbles have been observed on the left side of the heart ina patient who was subsequently shown to have a minor septal defect, orpatient foramen ovale (“PFO”), i.e. a hole in the heart. The patientreported experiencing a transient visual disturbance. This issignificant because, once on the left side of the circulation, thebubbles can progress to the brain, where they may cause microinfarcts.

At present it is believed that screening all patients for even the mostminor PFO is not really feasible for an elective procedure such asvaricose vein treatment and may not even be possible. The techniquesrequired would be fairly sophisticated and possibly quite invasive.Furthermore this would increase the time required for the procedure andpreclude treatment of patients having such PFOs, of which it is believedthere are significant numbers.

In the light of these unexpected findings, considerable furtherfundamental research has been carried out by the inventors.

Experiments using animal models have been carried out by the inventorsand internationally recognized experts in their field have beencommissioned to carry out detailed mathematical modeling of the behaviorof oxygen, carbon dioxide and nitrogen bubbles in blood. In vitro workto measure the absorption of gases in fresh human venous blood has alsobeen carried out by the inventors. As a result it has become clear that,contrary to previous thinking by the inventors, and in stark contrast tothe thinking of almost every practitioner currently preparingextemporaneous foam for use in varicose vein treatment, even thesmallest volume of nitrogen may be significant in causing persistentbubbles.

Furthermore, recent studies have been published further confirming thatair foams previously suggested in the art are causing some complicationsfor certain patient groups. For example, Dr. Philip Kritzinger, MD haspresented case studies where foams for sclerotherapy of veins that weremade using air as the gas phase may lead to seizures and myocardialinfarction in some geriatrics or patients at high risk of coronaryproblems.

The inventors have now determined that in order to produce a productsuitable for administration to patients without the need for lengthy PFOscreening methodology it may be required to reduce the amount ofnitrogen to upper limits that were previously unrecognized.

Further developments of the canister system described in WO00/72821-A1and WO002/41872-A1 have been devised, specifically raising thepercentage of carbon dioxide in the foam and reducing the nitrogenpresent in the foam to near zero. To compensate for the deleteriouseffects of the highly soluble carbon dioxide, the size of the aperturesin the mesh has been reduced to 5 microns from 20 microns. Canisters ofthis design have been made in reasonably large numbers for testing.Initially, double canister systems as described above were prepared byflushing the canisters with the desired gas before sealing andpressurizing them. This product generated a foam with between 1% and 2%nitrogen. Further research has led the inventors to believe, however,that even this level may be too high.

Recognizing that there will always be impurity no matter what techniqueis adopted for making the foam, the inventors believe that a sclerosingfoam having a percentage by volume of nitrogen gas within the range0.01% and 0.8% is both clinically safe and consistently reproducible. Itmay be possible routinely to produce canisters with as little as 0.0001%nitrogen gas. Examples presented below illustrate themanufacture/preparation and also the clinical effects of such a foam.

The inventors also recognize that techniques such as those describedabove using syringes, together with a variety of other techniques forextemporaneous preparation of sclerosing foam which have been developedsince the Cabreras disclosure, may have their place in the field of foamscleropathy. These techniques may well provide a less expensive optionthan a canister product. The inventors believe that it is possible toprepare foams having a very low percentage of nitrogen, as set outabove, using these types of technique as well as using a canistersystem.

According to the present invention, a foam comprising a liquid phase anda gas phase wherein the liquid phase comprises at least one sclerosingagent and the gas phase consisting essentially of gaseous nitrogenpresent in an amount ranging from 0.0001% to 0.8% by volume and at leastone physiologically acceptable gas. In a further embodiment, the gasphase may further comprise other gases such as trace gases as definedbelow, which may also effect at least one of at least one of thedensity, half life, viscosity, and bubble size of the resulting foam. Asused herein, consisting essentially of means that one or more additionalcomponent may be added, such as gas, that would not substantially effectat least one of the density, half life, viscosity, and bubble size ofthe resulting foam.

“Physiologically acceptable gas” means gases which are relativelyreadily absorbed by the blood or which can pass rapidly across thepulmonary gas exchange membranes. Specifically, oxygen, carbon dioxide,nitrous oxide and helium are contemplated. Other gases, which may or maynot fall within the terms of the definition of physiologicallyacceptable gases, may be used at least in small quantities, e.g. xenon,argon, neon or others. As used herein, a gas phase that is“substantially” a specific gas, such as “substantially O2”, refers to agas phase that is O2 with the impurities normally found in commercialmedical grade O2 gas. Gases which are found only at trace concentrationsin the atmosphere (such as those just mentioned) may be useful toincorporate in the formulation, e.g. at relatively low concentrations ofbetween about 0.1% and 5%, in order to facilitate the detection ofleaks.

In another embodiment, the said other gas consists essentially ofoxygen. Another possibility is for the other gas to consist essentiallyof oxygen and a minor proportion, preferably 40% or less of carbondioxide, still more preferably 30% or less of carbon dioxide. Forexample, the gas phase may comprise at least 50% O2, such as forexample, as 70%, 80%, 90% and 99% O2. In another embodiment, it may alsocomprise a major portion of CO2, such great than 50% CO2, such as 70%,80%, 90% and 99% CO2. In these cases, between 0.1% and 5% of the othergas may be constituted by gases which are only found at trace levels inthe atmosphere, e.g. argon, helium, xenon, neon. Alternatively the gasmay be substantially 100% nitrous oxide or a mixture of at least two ofoxygen, nitrous oxide and carbon dioxide.

For the purpose of this application various other terms have thefollowing definitions: A sclerosant liquid is a liquid that is capableof sclerosing blood vessels when injected into the vessel lumen andincludes without limitation solutions of polidocanol, tetradecylsulphate, ethanolamine oleate, sodium morrhuate, hypertonic glucosatedor glucosaline solutions, chromated glycerol, iodated solutions.Scleropathy or sclerotherapy relates to the treatment of blood vesselsto eliminate them. An aerosol is a dispersion of liquid in gas. A majorproportion of a gas is over 50% volume/volume. A minor proportion of agas is under 50% volume/volume. A minor amount of one liquid in anotherliquid is under 50% of the total volume. Atmospheric pressure and barare 1000 mbar gauge. Half-life of a foam is the time taken for half theliquid in the foam to revert to unfoamed liquid phase.

As suggested by Cabrera and discussed above, one could use oxygen ormixtures of oxygen and carbon dioxide of the gas component. Carbondioxide is very soluble in water (and hence blood) and oxygen is notvery soluble in water but is taken up relatively rapidly by haemoglobinin blood. The present inventors have also done studies that have shownthat CO2 and O2 are taken up in blood much faster than N2 or air.However, foams made solely with carbon dioxide, or other highlywater-soluble gases, tend to be very unstable and do not last longenough to be usable. Because CO2 foams have a very short half life,foams with a high concentration of CO2 have not been used in the past toprepare foams for sclerotherapy.

For example, a predominantly insoluble gas mix such as air will yield astable, staff foam with a half separation time of 150-200 seconds usingthe Cabrera method. However, highly soluble gas atmospheres such as 100%CO2 yield foams with much shorter half separation times. It is thoughtthat the rapid dissolution and transport of CO2 in the lamellar cellwalls of the foam is responsible for the reduced stability of some CO2foams. This allows the smaller, high pressure bubbles of the foam torapidly transfer all their gas content to adjacent larger low pressurebubbles, which then rise through the foam to burst or accumulate at asurface. This process is called Ostwalt ripening, and with all-CO2 foamsthe liquid cell wall is no longer a significant barrier to diffusionbetween adjacent bubbles at different Laplace pressures. Drainage andseparation of foam into gas and liquid components is also influenced bythe viscosity of the liquid component.

Oxygen foams do not have this problem, but the injection of oxygen gashas been reported to be dangerous and, in fact, has been said to bealmost as dangerous as air when injected into the venous system. See,for example, Moore & Braselton “Injections of Air and carbon Dioxideinto a Pulmonary Vein”, Annals of Surgery, Vol 112, 1940, pp 212-218.While another study suggests that for some high risk patient groups highconcentrations of O2 in foams used for sclerotherapy may increase therisk of side effects.

Recent studies have also suggested that foams for sclerotherapy madewith high concentrations of N2 or O2 may lead to potential side effectsin certain patient groups. More specifically, one study suggests thathigh concentrations of nitrogen may lead to a higher risk of arterialembolism in certain patient populations.

The present inventors, however, have discovered that it is possible tomake an effective foam for use in sclerotherapy using highconcentrations of CO2 as the gas phase and the addition of a viscosityenhancing agent to the liquid phase. The addition of a viscosityenhancing agent, however, while increasing the half life of a CO2 foam,also increases the density of the foam. Too high of a density can hindera foams ability to displace blood and therefore be an effective foam forsclerotherapy. It was discovered that a balance of density and half lifeenables the production of an effective foam. In one embodiment, thisbalance of density and half life is achieved by increasing the viscosityenhancing agent to at least 20% wt/wt and using various methods asdescribed herein to produce the foam.

Viscosity enhancing agents include any agent that will increase theviscosity of the liquid phase, such as PVP and glycerol. In oneembodiment, at least 20% wt/wt viscosity enhancing agent is present inthe liquid phase, such as for example 25%, 30%, 35%, 40%.

Viscosity of the liquid phase before production of the foam may also bea factor in the half life of the foam. For example, increasing viscosityof the liquid phase will increase half life of the foam. However, ahigher viscosity may raise the density of the resulting foam in somesystems.

Thus, in a further embodiment, the foam of the invention comprises aliquid phase and a gas phase wherein the liquid phase comprises at leastone sclerosing agent and is at least 20% wt/wt of at least one viscosityenhancing agent; and the gas phase comprises at least 50% CO2; andwherein the foam has a density less than 0.25 g/cm and half life ofgreater than 100 secs. The gas phase may, for example be at least 75%CO2, such as at least 90% CO2, such as at least 99% CO2. In oneembodiment, the gas phase consists essentially of CO2.

The foam, for example, may have a half life of at least 90 second, suchas at least 100, such as at least 110, such as at least 120 seconds,such as at least 130 seconds, such as at least 140 seconds, such as atleast 150 seconds, such as at least 160 seconds, such as at least 170seconds, such as at least 180 seconds, and such as at least 3.5 minutes.The density of the foam may range from 0.07 to 0.22, such as 0.07 to0.19 g/ml, 0.07 to 0.16 g/ml, such as 0.08 to 0.14, also such as 0.8 to0.15 g/ml, such as 0.9 to 0.13 g/ml and such as 0.10 to 0.14 g/ml. Thegas phase may further comprises another physiologically acceptable gasthat is dispersible in blood, such as O2. The viscosity of the liquidphase may range from 2.0 to 10 cP, such 2.0 to 7.0 cP, such as 2.0 to5.0 cP, such as 2.0 to 3.5 cP, such as from 2.0 to 3.0 cP, such as 2.0to 2.5 cP.

FIGURES

FIG. 1 is a schematic representation of a syringe barrel part of a firstembodiment of device in accordance with the first aspect of theinvention, showing it in a sealed state for storage;

FIG. 2 is a schematic representation of a cartridge for use with thesyringe barrel of FIG. 1;

FIG. 3 is a schematic representation of a modified cartridge for usewith the syringe barrel of FIG. 1;

FIG. 4 is a further schematic representation of the syringe barrel ofFIG. 1 with a cartridge of the type shown in FIG. 3 being installed;

FIG. 5 is a further schematic representation of the syringe barrel ofFIG. 1 with a foaming unit and plunger stem fitted;

FIG. 6 is a schematic representation of the syringe, cartridge andfoaming device of FIG. 5, with the plunger stem of the syringe partiallydepressed;

FIG. 7 is a schematic representation of a second embodiment of device inaccordance With the first aspect of the invention, comprising chargedsyringe with foaming unit fitted;

FIG. 8 is a schematic representation of the device of FIG. 7 installedin a syringe driver for generation and delivery of foam at a controlledrate;

FIG. 9 is a schematic representation of a third embodiment of deviceaccording to the invention;

FIG. 10 is a schematic representation of the device of FIG. 9 fitted toa motorized driver;

FIG. 11 is a plan view of a mesh element of an embodiment of a foamingunit forming part of the invention;

FIG. 12 is a side sectional view along the line I-I in FIG. 11; and

FIG. 13 is a side sectional view of an embodiment of foaming unitforming part of the invention.

FIG. 14 shows a cross-sectional view of a pre-pressurized container forthe generation of therapeutic foam according to the invention, asdisclosed in WO 00/72821-A1 and further described below.

FIG. 15 shows a shows a cross-sectional view of a device comprising acontainer provided with engaging means and a mesh stack shuttleaccording to the invention, as disclosed in WO 02/41872-A1 and furtherdescribed in below.

FIG. 16 shows a graph to compare the results from the four bi-canconditions tested in Example 3 below, showing the effect of gas mix, gaspressure and shuttle mesh on foam density and half-life. Control 1 usesa 75% CO2/25% N2 gas mixture in a 0.5 bar canister with a 5 μm mesh;Test 1 uses the same gas mixture with a 5 μm mesh; Control 2 uses 100%CO2 in a 1.2 bar canister with the 20 μm mesh; Test 2 uses the same gaswith a 5 μm mesh.

FIG. 17 shows a graph of the average number of bubbles by diameter fromthe four bi-can conditions tested below.

FIG. 18 shows a graph of the proportion of bubbles by diameter from thefour bi-can conditions tested in below.

FIG. 19 shows a graph of the average volume of bubbles by diameter fromthe four bi-can conditions tested in below.

FIG. 20 shows a graph of the proportion of bubbles by diameter from thefour bi-can conditions tested in below.

FIG. 21 shows a graph to compare the results from the four bi-canconditions tested below, showing the effect of shuttle mesh size onhalf-separation time and density.

FIG. 22 shows the effects of (a) glycerol concentration on viscosity ofthe liquid phase before mixing with the gas phase to form a foam and (b)the effects of various viscosity enhancing agents on viscosity of theliquid phase.

FIG. 23(a, b, and c) shows the effects of various viscosity enhancingagents on the density and half life of a Cabrera foam.

DETAILED DESCRIPTION

For the purpose of this application terms have the followingdefinitions: A sclerosant liquid is a liquid that is capable ofsclerosing blood vessels when injected into the vessel lumen.Scleropathy or sclerotherapy relates to the treatment of blood vesselsto eliminate them. An aerosol is a dispersion of liquid in gas. A majorproportion of a gas is over 50% volume/volume. A minor proportion of agas is under 50% volume/volume. A minor amount of one liquid in anotherliquid is under 50% of the total volume. Atmospheric pressure and barare 1000 mbar gauge. Half-life of a foam is the time taken for half theliquid in the foam to revert to unfoamed liquid phase.

In one embodiment, the foam is such that 50% or more by number of itsgas bubbles of 25 μm diameter and over are no more than 200 μm diameter.

Half-life is conveniently measured by filling vessel with a known volumeand weight of foam and allowing liquid from this to drain into agraduated vessel, the amount drained in a given time allowingcalculation of half-life i.e. of conversion of foam back into itscomponent liquid and gas phases. This is preferably carried out atstandard temperature and pressure, but in practice ambient clinic orlaboratory conditions will suffice.

As used here, the viscosity is determined by Brookfield DVII+Pro made byBrookfield Engineering Labs at room temperature.

In one embodiment, the gas/liquid ratio in the mix is controlled suchthat the density of the foam is 0.09 g/mL to 0.16 g/mL, more preferably0.11 g/mL to 0.14 g/mL.

In another embodiment, the foam has a half-life of at least 100 seconds,such as for example, 2 minutes, 2.5 minutes, and 3 minutes. Thehalf-life may be as high as 1 or 2 hours or more, but is preferably lessthan 60 minutes, more preferably less than 15 minutes and mostpreferably less than 10 minutes.

In one embodiment, the mixture of gas and sclerosant liquid is in theform of an aerosol, a dispersion of bubbles in liquid or a macrofoam. Bymacrofoam is meant a foam that has gas bubbles that are measured inmillimeters largest dimension, e.g. approximately 1 mm and over, andover such as can be produced by lightly agitating the two phases byshaking. In another embodiment, the gas and liquid are provided in theform of an aerosol where a source of pressurized gas and a means formixing the two is provided to the point of use. It may be that amacrofoam is first produced where the liquid and gas are broughttogether only at the point of use.

The ratio of gas to liquid used in the mixture may be important in orderto control the structure of the foam produced such that its stability isoptimized for the procedure and the circumstances in which it is beingcarried out. For some foams, one may mix 1 gram sclerosant liquid withfrom approximately 6.25 to 14.3 volumes (STP), more preferably 7 to 12volumes (STP), of gas.

In one embodiment, the physiologically acceptable blood dispersible gascomprises a major proportion of carbon dioxide and/or oxygen. In someembodiments, the foam may comprise a minor proportion of nitrogen. Whilea proportion of nitrogen may be present, as in air, the presentinvention provides for use of carbon dioxide and/or oxygen withoutpresence of nitrogen.

In one form the gas used is a mixture of carbon dioxide and otherphysiological gases, particularly containing 3% vol/vol or more carbondioxide, such as from 10 to 90% carbon dioxide, such as from 30 to 50%carbon dioxide. The other components of this gas may be oxygen.

Another form of gas comprises 50% vol/vol or more oxygen, the remainderbeing carbon dioxide, or carbon dioxide, nitrogen and trace gases in theproportion found in atmospheric air. One gas is 60 to 90% vol/vol oxygenand 40 to 10% vol/vol carbon dioxide, another is 70 to 80% vol/voloxygen and 30 to 20% vol/vol carbon dioxide. One embodiment is 99% ormore oxygen.

Preferably the sclerosing agent is a solution of polidocanol or sodiumtetradecylsulfate in an aqueous carrier, e.g. water, particularly in asaline. More preferably the solution is from 0.5 to 5% v/v polidocanol,preferably in sterile water or a physiologically acceptable saline, e.g.in 0.5 to 1.5% v/v saline. Concentration of sclerosant in the solutionwill be advantageously increased for certain abnormalities such asKlippel-Trenaunay syndrome.

Polidocanol is a mixture of monolauryl ethers of macrogols of formulaC12C25(OCH2CH2)nOH with an average value of n of 9. It will be realizedthat mixtures with other alkyl chains, oxyalkyl repeat units and/oraverage values of n might also be used, e.g. 7 to 11, but that 9 is mostconveniently obtainable, e.g. from Kreussler, Germany, e.g. asAethoxysklerol™, a dilute buffered solution of polidocanol.

The concentration of sclerosant in the aqueous liquid is a 1-3% vol/volsolution, such as polidocanol, in water or saline, such as about 1%vol/vol. The water or saline also, in some cases at least, contain 24%vol/vol physiologically acceptable alcohol, e.g. ethanol. Saline may bebuffered. Some buffered saline is phosphate buffered saline. The pH ofthe buffer may be adjusted to be physiological, e.g. from pH 6.0 to pH8.0, more preferably about pH 7.0.

The sclerosant may also contain additional components, such asstabilizing agents, e.g. foam stabilizing agents, e.g. such as glycerol.Further components may include alcohols such as ethanol.

In one embodiment, ranges for the gaseous nitrogen volume at are 0.0001%to 0.75%, such as 0.7%, such as 0.6%, and such as 0.5%. Although from atheoretical viewpoint it may be desirable to eliminate as much nitrogenas possible, it is also understood that since we live in an atmosphereof 80% nitrogen there are difficulties in consistently making a foamwith a very high degree of purity with regard to nitrogen gas.Accordingly, the lower end for the range of nitrogen impurity which ispreferable (from the point of view of being easier and/or less expensiveto manufacture) is 0.0005%, more preferably 0.001%, still morepreferably 0.005%, 0.01%, 0.05%, 0.1%, 0.2%, 0.3% or 0.4%. As will beapparent from the examples below, each incremental increase in the lowerend of the range may result in a purifying step being taken out of themanufacturing procedure, with resulting cost savings.

Also according to the invention is provided a canister system adapted todispense a foam and whose contents consist of a liquid phase and a gasphase, wherein the liquid phase comprises a sclerosing agent and the gasphase consists of a minor proportion of nitrogen gas and a majorproportion of other gas, preferably physiologically acceptable gas, suchthat the gas phase of a foam produced by the canister system consists ofbetween 0.0001% and 0.8% nitrogen gas. The other possible ranges for thenitrogen gas component, as recited above, also apply.

It will be appreciated that the term “canister system” can mean either asingle canister containing a liquid and a gas for dispensing to generatea foam, or a two canister arrangement as described above, where gas isstored in one canister and liquid, optionally together with gas, inanother.

In one embodiment, said minor proportion of nitrogen gas in the canisteris also 0.0001% to 0.8% by volume of the total gas volume in thecanister, or optionally the other ranges recited above.

In another embodiment, the canister includes an element through whichthe liquid and gas contents pass in order to dispense foam. In oneembodiment, this element has apertures of approximately 0.1 to 15 microndiameter, more preferably 1-7 micron, still more preferably about 5micron.

Another aspect of the present invention is a method for producing a foamsuitable for use in scleropathy of blood vessels, particularly veins,characterized in that it comprises passing a mixture of gas and anaqueous sclerosant liquid through one or more passages having at leastone cross-sectional dimension of from 0.1 to 15 μm, the ratio of gas toliquid being controlled such that a foam is produced having a density ofbetween 0.07 g/mL to 0.19 g/mL and a half-life of at least 100 seconds,such as 2 minutes, such as 2.5 minutes.

Preferably, the said one or more passages have at least onecross-sectional dimension of from 1-7 micron, more preferably about 5micron.

In accordance with the original specification (as set out inWO00/72821-A1), the foam is preferably such that 50% or more by numberof its gas bubbles of 25 μm diameter and over are no more than 200 μmdiameter. Again in accordance with the original specification inWO00/72821-A1, preferably the method provides a foam characterized inthat at least 50% by number of its gas bubbles of 25 μm diameter andover are of no more than 150 μm diameter. More preferably at least 95%of these gas bubbles by number are of no more than 280 μm diameter.Still more preferably at least 50% by number of these gas bubbles are ofno more than 130 μm diameter and still more preferably at least 95% ofthese gas bubbles by number are of no more than 250 μm diameter.

In one embodiment, the gas comprises from 1% to 50% carbon dioxide,preferably from 10% to 40%, more preferably from 20% to 30%.Surprisingly, it has been found that by using a smaller aperture sizefor the mesh, foams having the specification set out in WO00/72821-A1can be made with gas mixtures having higher proportions of carbondioxide and correspondingly lower proportions of insoluble gases such asnitrogen. Carbon dioxide may be a desirable component of the gas mixturedue to its extreme solubility, greater than that of oxygen.

Also according to the invention a method for angiologic treatmentcomprises injecting an effective amount of a sclerosing foam whosegaseous component consists of between 0.0001% and 0.8% by volume gaseousnitrogen, the balance being other gas, preferably physiologicallyacceptable gas. The other possible ranges recited above for thepercentage of nitrogen apply and the options for the other gases recitedabove apply.

Preferably the method of treatment comprises the injection of 10 ml to50 ml of foam in a single injection, preferably 15 ml to 50 ml, morepreferably 20 ml to 50 ml, still more preferably 30 ml to 50 ml of foam.

According to the invention a method of treatment of the human greatersaphenous vein comprises treating substantially the entire greatersaphenous vein of one leg with a single injection of foam as describedabove.

According to the invention a method of treatment of a blood vessel ofdiameter 7 mm or greater so as to cause damage to the endothelium of thevessel comprises injecting foam as described above.

A further factor in the inventors' developing understanding of thebehavior in blood of bubbles comprising soluble gases is the phenomenonof nitrogen diffusing out of blood and adjacent tissues and into thebubbles due to a difference in the partial pressure of nitrogen in thebubbles as compared with that in the surrounding blood and tissues. Thisphenomenon will generally only occur when the partial pressure ofnitrogen in the bubble is lower than that in the surrounding blood andtissues.

It appears that carbon dioxide, and to a lesser extent oxygen, willdiffuse out of the bubble and go into solution in the surrounding bloodrelatively very quickly, so that the bubble will quite quickly reach apoint where the partial pressure of nitrogen in the bubble will behigher than that in the surrounding blood and tissues and, ultimately,the bubble will become substantially pure nitrogen. As soon as thenitrogen partial pressure gradient is reversed, nitrogen will come outof the bubble and into solution in the blood, though this will happenrelatively slowly because of the low solubility of nitrogen. Thisphenomenon will also be influenced by increasing saturation of thesurrounding blood with nitrogen, if this occurs to a significant extent.This phenomenon potentially affects the partial pressure gradient ofnitrogen in the blood and may also mean that a limit for dissolution ofnitrogen is reached if the surrounding blood becomes fully saturatedwith nitrogen.

It is not at present understood to what extent localised saturation ofblood with nitrogen is a factor in the dissolution of the bubbles in adispersing foam. Since the bloodstream in constant motion, however, itis assumed that this effect will only ever be transient and will notunduly affect the overall picture of nitrogen dissolution.

It appears that the initial phase of rapid dissolution of carbon dioxideand/or oxygen is critical: the shorter this period, the smaller thevolume of nitrogen which is able to diffuse into the bubble.

There are several possibilities for eliminating residual bubbles orreducing them in size and/or number (apart from reducing the initialquantity of nitrogen in the gas phase of the foam). One of these is tomake the bubbles as small as is practical. The smaller the bubble, thefaster the carbon dioxide and/or oxygen will dissolve out of the bubbleand therefore the shorter the time available for nitrogen from the bloodto diffuse into the bubble before the partial pressure gradient fornitrogen reverses in favor of nitrogen diffusing out of the bubble.

Another is that of the patient breathing oxygen or air enriched withoxygen, which has the effect of increasing the oxygen partial pressurein the blood at the expense of the nitrogen partial pressure. Thistechnique is known in the fields of diving and space exploration, whereit has been used to reduce the risk of the “bends”, i.e. the tendency ondepressurisation for nitrogen to come out of solution in body tissues(as opposed to the blood in blood vessels which is what we are concernedwith here). As far as the inventors are aware, it has never previouslybeen proposed to use this technique in connection with injecting gasesinto the vascular system.

According to an aspect of the invention a sclerosant foam is composed ofbubbles of which, ignoring bubbles of 1 micron or less diameter, 95% ormore are of 150 micron diameter or less and 50% or more are of 100micron diameter or less. Preferably, 95% or more of the bubbles are of100 micron diameter or less and 50% or more of the bubbles are of 50micron diameter or less. More preferably, 95% or more of the bubbles areof 75 micron diameter or less and 50% or more of the bubbles are of 30micron diameter or less. Still more preferably, 95% or more of thebubbles are of 60 micron diameter or less and 70% or more of the bubblesare of 30 micron diameter or less. Examples are presented below showinghow foams with these sorts of bubble distributions have been made.

These very small bubble foams have only to date been obtained by theinventors by having a relatively dense formulation of the order of 0.3to 0.5 g/ml, with a relatively high ratio of liquid to gas. Such a wetfoam is still considerably less dense than blood and therefore will bebuoyant when in a vein full of blood. It is speculated that this buoyantcharacteristic may to some extent be responsible for the advantageousbehavior of foam in the vascular system in terms of displacing blood.However, the dense foams produced to date by the inventors behaveessentially as a liquid in terms of their Theological properties—theyare not “stiff”.

It is not impossible that these dense but somewhat fluid foams may havea sufficiently good therapeutic effect to be useful and may alsoeliminate or reduce the residual gas problem. However, it is probablethat the Theological properties of the foam in blood are important, andthat a “stiff” foam is desirable effectively to displace blood and thusallow consistent, uniform application of the active to the interior ofthe vessel wall. For this reason it may be desirable to add a furtheringredient to the foam in order to increase its stiffness/viscosity,either by adding a viscosity-enhancing additive to the formulation or byadding an agent which increases the foaming capacity of the formulation.

Such ingredients could be, without limitation, Polysorbate 20,Polysorbate 80 or Polygeline. Alternatively, glycerol and PVP may beadded.

A foam with a bubble size distribution falling within the definitionsset out above may be created by passing gas and liquid repeatedlythrough a fine mesh, e.g. a 5 micron mesh. Repeated passages through themesh reduce the bubble size, though there appears to be a limit on this.

It is envisaged that other known techniques for agitating a gas andliquid mixture at high energy could be applied to make even finerbubbles. For example sonic or ultrasonic agitation of a mixing stream ofgas and liquid could be used, or alternatively a mixture of beating thegas and liquid by mechanical means, supplemented by the application ofsonic or ultrasonic energy.

The inventors have also prepared a foam having an average bubble size inthe range 50 micron to 80 micron by adapting a canister to alter theratio of liquid and gas being passed through a mesh.

A further aspect of the invention is a pressurized canister productadapted to dispense a sterile gas and sclerosing liquid mixture inpredetermined proportions into a syringe, as a solution to some of theissues with extemporaneous preparation of foam. Thus a pressurizedcanister is provided—which may be of any suitable material such asanodized aluminum or even glass—containing sterile gas and sclerosingliquid and arranged to dispense the correct volume of liquid and gasinto a syringe. It is envisaged that the canister would contain sterilegas with a very low nitrogen concentration etc. as defined above. Thecanister may have a pierceable septum for puncturing with a hypodermicneedle, or it may have a break seal which is arranged to be broken byinsertion of a syringe luer nozzle.

In the latter case, a syringe luer nozzle could be inserted into thecanister in a sealing fashion, with the syringe nozzle pointing upwards.Liquid in the canister would be dispensed first under pressure, followedby equalization of the pressure in the canister and syringe. Thepressure and volume of gas in the canister could of course be arrangedso that the correct proportions of gas and liquid are dispensed.Alternatively, the canister could be provided with an internal dip tubeso that the same effect is achieved with the canister in an uprightorientation.

Also according to the invention is provided a method of preparing asclerosing foam which includes the step of cooling the ingredients ofthe foam to a sub-ambient temperature prior to generation of the foam. Asuitable temperature range might be 0 to 15 degrees Celsius, preferably0 to 10 degrees, more preferably 3 to 7 degrees. Decreasing temperatureincreases liquid viscosity and, in this way, the inventors believe thehalf life of the foam could be extended. Since, during decay of a foam,the bubble size tends to increase, this methodology may help reduce theaverage size of bubbles over time in the body and thereby reduceresidual bubbles.

Also according to the invention, and in line with the reasoningpresented earlier, a method of angiologic treatment of a patientcomprises causing the patient to breathe oxygen gas or oxygen-enrichedair for a predefined period prior to injection of foam as describedabove. Preferably the predefined period is 1 to 60 minutes, morepreferably 1-20 minutes, more preferably 5-10 minutes.

Another embodiment of the present invention provides a foam, that, forexample, can be used in the elimination of blood vessels and vascularmalformations, that are made available by the method and devices of theinvention, comprising a physiologically acceptable gas that is readilydispersible in blood together with an aqueous sclerosant liquid whereinin that the foam has a density of from 0.07 to 0.19 g/cm.

In one embodiment, the foam is capable of being passed down a 21 gaugeneedle without reverting back to gas and liquid by more than 10%, basedon liquid content reverting back to unfoamed liquid phase.

Half-life is conveniently measured by filling vessel with a known volumeand weight of foam and allowing liquid from this to drain into agraduated vessel, the amount drained in a given time allowingcalculation of half-life i.e. of conversion of microfoam back into itscomponent liquid and gas phases. This is preferably carried out atstandard temperature and pressure, but in practice ambient clinic orlaboratory conditions will suffice.

Most conveniently the funnel is pre-equilibrated in a water bath toensure a temperature of 25° C. before drying and application of foam.Placing of a foam filled syringe upside down, without its plunger, abovethe funnel leading into a graduated receptacle allows convenientmeasurement of this parameter.

In one embodiment, the foam, on passage through said needle, does notrevert back to unfoamed liquid by more than 5% based on liquid content,still more preferably by no more than 2%. This is measured by measuringthe change in volume of the foam versus the liquid.

In one embodiment, the foam is capable of being passed down a needlewhile retaining at least 50% by number of its gas bubbles of at least 25μm diameter at no more than 200 μm diameter. This is convenientlymeasured under ambient conditions, more preferably at STP.

In one embodiment, the gas includes less than 40% v/v nitrogen.Preferably the density of the foam is from 0.09 to 0.16 g/mL, morepreferably 0.11 g/mL to 0.14 g/mL.

In one embodiment, the foam density, which is a measure of liquid/gasratio, is from 0.13 to 0.14 g/cm and the half-life is at least 2.5minutes. The foam more preferably does not move outside of itsparameters of bubble size set out above in such time.

In one embodiment, the gas consists of at least 50% oxygen or carbondioxide, more preferably 75% or more oxygen or carbon dioxide and mostpreferably at least 99% oxygen or carbon dioxide, e.g. substantially100% oxygen or carbon dioxide. Preferably the oxygen or carbon dioxideis medical grade.

As discussed above, addition of glycerol to the aforesaid sclerosantimparts a longer half-life to the resultant foam. However, glycerol mayincrease density and also produces a tendency for the meshes to block upwhen using a mesh device as described above, so should be used carefullywhere the device it is produced from may be used multiple times or thebag-on-valve concept is used.

The invention also provides:

-   -   a method of treating a patient in need of sclerotherapy of a        blood vessel comprising administering a foam as described above        to that blood vessel; use of a foam described above for the        manufacture of a medicament for sclerotherapy; and a foam as        described above for use in therapy.

Accordingly the one aspect of the present invention provides a methodfor producing a foam suitable for use in scleropathy of blood vessels,particularly veins, characterized in that it comprises passing a mixtureof a physiologically acceptable blood dispersible gas and an aqueoussclerosant liquid through one or more passages having at least onecross-sectional dimension of from 0.1 to 15 μm, the ratio of gas toliquid being controlled such that a foam is produced having a density ofbetween 0.07 g/mL to 0.19 g/mL and a half-life of at least 100 seconds.

Apparatuses for Generating Foam

There are a number of issues with the current practice of extemporaneouspreparation of foam, the use of air as the gas being only one of these.Other issues are the consistency of the product, which is by naturehighly variable because it depends on the physician selecting the gas toliquid ratio and then pumping the gas and air mixture a given number oftimes and/or at a given speed to obtain the right product. Foams arehighly variable and different bubble sizes and densities will havedifferent safety and efficacy profiles.

Very recently, a machine has been made available which is designed toreceive two syringes and apply a given number of pumps at a given rateto achieve a roughly consistent product. The machine is called“Turbofoam”® but the inventors are not at present aware who is marketingthe machine. Two syringes are loaded into it (one of which is loadedwith sclerosant solution). When activated, the machine automaticallydraws a predetermined quantity of atmospheric gas into the syringes andcycles the syringes until a foam of the desired properties is made.

Clearly, the arrangement described above addresses at least the issuesof reproducibility of the foam as regards the gas/liquid ratio (providedthe correct amount of liquid is loaded initially by the user) and alsothe number and speed of cycles. However, it is obviously also quiteinconvenient in many respects and sterility may also be compromised bybuild up of bacteria in the gas channels of the machine, for example.

The solution proposed by the inventors is to provide a sterile packcontaining one or two syringes, optionally together with any connectorsetc. The syringe or syringes is/are pre-loaded with the correct volumesof gas and sclerosing liquid. Most syringes are made from plasticsmaterial such as polypropylene which allows gas to permeate through itover time. Therefore, the packaging is preferably substantiallygas-impermeable and the atmosphere in the pack is preferablysubstantially the same composition as the gas pre-loaded into thesyringe. This sort of packaging is well known in itself and examplesinclude metallized plastic sheeting e.g. an aluminum and polyethylenelaminate.

According to one aspect of the invention, there is provided asubstantially sterile pack comprising:

a syringe charged with a liquid sclerosing agent and a gas mixturecomprising physiologically acceptable gas, such as, for example, between0.0001% and 0.8% gaseous nitrogen with the balance being other gas, suchphysiologically acceptable gas; and

a gas atmosphere inside the pack having substantially the samecomposition as the said gas mixture in the syringe.

In one embodiment, the gas mixture consists of 0.001% to 0.8% gaseousnitrogen, preferably 0.01% to 0.8%, more preferably 0.01% to 0.7%, stillmore preferably 0.01% to 0.6%.

In one embodiment, the said other gas is oxygen, carbon dioxide or amixture thereof. Optionally, a small percentage (e.g. 0.1 to 5%) of atracer gas, which is not found in significant amounts in the atmosphere,is added to allow leaks to be detected. Such a gas might be e.g. helium,neon, argon, xenon or any other gas which is found in traceconcentrations (0.01%) in atmospheric air.

To avoid contamination, the pack contents may be at slightly aboveatmospheric pressure. This may be achieved by manufacturing the pack atan ambient temperature below standard room temperature. Once the packenters normal ambient surroundings, the temperature increase of theatmosphere inside the pack will ensure a slight overpressure.

Manufacture of the packaged product would be carried out in asepticconditions, using techniques standard in that field.

This pre-packaged product may include one syringe of the type comprisinga barrel, a first plunger and a second plunger, the second plungerhaving an apertured plunger head which is adapted to be movable withinthe barrel independently of the first plunger.

Alternatively the syringe may be a conventional one, containing anappropriate amount of gas as described above. A further syringecontaining sclerosing agent could be provided in the same or a differentpack, together with the connectors, three way valves, etc. necessary toperform any of the known techniques for extemporaneous foam preparation.

In use, the pack is opened and the usual technique followed forgenerating foam, without the need to measure out liquid or gas. In thecase of a two syringe technique, the syringes can be supplied readyconnected, to increase convenience and remove a potential source ofcontamination.

Optionally, the pack may include a syringe connector which incorporatesa fine mesh with apertures of 1-200 micron, preferably 2 to 50, morepreferably 3 to 20 micron maximum dimensions. Alternatively, if a singlesyringe device is used, the apertures in the plunger may be provided bya mesh with pores of these proportions.

Optionally, the package could constitute a cartridge for a foamgenerating machine similar to the “Turbofoam”® described above.

A further solution to the issues with extemporaneous foam preparationhas been proposed by the inventors. This is to provide a pressurizedcanister—which may be of any suitable material such as anodized aluminumor even glass—containing sterile gas and sclerosing liquid and arrangedto dispense the correct volume of liquid and gas into a syringe. It isenvisaged that the canister would contain sterile gas as defined above.The canister may have a pierceable septum for puncturing with ahypodermic needle, or it may have a break seal which is arranged to bebroken by a syringe luer nozzle.

In the latter case, a syringe luer nozzle could be inserted into thecanister in a sealing fashion, with the syringe nozzle pointing upwards.Liquid in the canister would be dispensed first under pressure, followedby equalization of the pressure in the canister and syringe. Thepressure and volume of gas in the canister could of course be arrangedso that the correct proportions of gas and liquid are dispensed.Alternatively, the canister could be provided with an internal dip tubeso that the same effect is achieved with the canister in an uprightorientation.

It is found that passing a stream of the sclerosant liquid and the gasunder pressure through one or more passages of 0.1 μm to 15 μm asdescribed provides a stable blood dispersible gas based sclerosantinjectable foam that was previously thought to be only producible bysupply of high amounts of energy using high speed brushes and blenders.

The aerosol, dispersion or macrofoam is preferably produced by mixingthe gas and liquid from respective flows under pressure. The mixingconveniently is carried out in a gas liquid interface element such asmay be found in aerosol canisters. The interface device may however bevery simple, such as a single chamber or passage of millimeterdimensions, i.e. from 0.5 to 20 mm diameter, preferably 1 to 15 mmdiameter, into which separate inlets allow entry of gas and liquid.Conveniently the interface is of design which is commonly found inaerosol canisters but which is selected to allow the correct ratio ofgas to liquid to allow formation of a foam of the presently defineddensity. Suitable inserts are available from Precision Valves(Peterborough UK) under the name Ecosol and are selected to produce theratio specified by the method above.

However, the mixing of gas and liquid may also be brought about within adip-tube leading from the sclerosant solution located in the bottom of apressurized container where holes in the dip-tube allow gas to enterinto a liquid stream entering from the bottom of the tube. In this casethe holes may be of similar diameter to the Ecosol holes. Such holes maybe conveniently produced by laser drilling of the dip-tube.

The one or more passages through which the aerosol or macrofoam soproduced are passed to produce the stable foam preferably have diameterof from 4 μm to 22 μm, more preferably from 5 μm to 11 μm where simplepassages are provided, such as provided by openings in a mesh or screen,e.g. of metal or plastics, placed perpendicular to the flow ofgas/liquid mixture. The passage is conveniently of circular orelliptical cross section, but is not necessarily so limited. A number ofsuch meshes or screens may be employed along the direction of flow.

Most preferably the passages are provided as multiple openings in one ormore elements placed across the flow. Preferably the elements are from 2to 30 mm diameter, more preferably 6 to 15 mm diameter, face on to theflow, with 5 to 65% open area, e.g. 2% to 20% open area for woven meshesand 20% to 70% open area for microporous membranes. Openings in a porousmaterial, such as provided in a perforated body, preferably provideseveral hundreds or more of such passages, more preferably tens orhundred of thousands of such passages, e.g. 10,000 to 500,000, presentedto the gas liquid mixture as it flows. Such material may be a perforatedsheet or membrane, a mesh, screen or sinter. Still more preferably anumber of sets of porous material are provided arranged sequentiallysuch that the gas and liquid pass through the passages of each set. Thisleads to production of a more uniform foam.

Where several elements are used in series these are preferably spaced 1to 5 mm apart, more preferably 2 to 4 mm apart e.g. 3 to 3.5 mm apart.For some embodiments of the present invention it is found that thepassage may take the form of a gap between fibers in a fibrous sheetplaced across the path of the gas/liquid flow, and the dimensiondescribed in not necessarily the largest diameter, but is the width ofthe gap through which the gas/liquid aerosol or macrofoam must flow.

Alternatively the method provides for passing the mixture of gas andliquid through the same set of passages, e.g. as provided by one or moresuch porous bodies, a number of times, e.g. from 2 to 2,000, morepreferably 4 to 200 times, or as many times as conveniently results in afoam of the required bubble size distribution set out above. It will berealized that the more times the foam passes through the meshes, themore uniform it becomes. Where multiple passes through the meshes arepossible, a large mesh size may be desirable, e.g., 20 to 300 μm, suchas 40 to 200 μm, such as 60 to 150 μm.

The pressure of the gas used as it is passed through the passages willdepend upon the nature of the mechanism used to produce the foam. Wherethe gas is contained in a pressurized chamber and passes only oncethrough the mesh, such as in an aerosol canister, in contact with theliquid, suitable pressures are typically in the range 0.01 to 9 bar overatmosphere. For use of meshes, e.g. 1 to 8 meshes arranged in series,having apertures of 10-20 μm diameter, 0.1 to 5 atmospheres over barwill, inter alia, be suitable. For use of 3-5 meshes of 20 μm apertureit is found that 1.5-1.7 bar over atmospheric is sufficient to produce agood foam. For a 0.1 μm pore size membrane, a pressure of 5 bar or moreover atmospheric pressure is preferred.

In one preferred form of the invention the passages are in the form of amembrane, e.g. of polymer such as polytetrafluoroethylene, wherein themembrane is formed of randomly connected fibers and has a ratedeffective pore size which may be many times smaller than its apparentpore size. A particularly suitable form of this is a biaxially orientedPTFE film provided by Tetratec™ USA under the trademark Tetratex™,standard ratings being 0.1 to 10 μm porosity. Preferred pore sizes forthe present method and devices are 3 to 7 μm. This material may belaminated with a porous backing material to give it strength and has theadvantage that one pass through may be sufficient to produce a foam thatmeets the use requirements set out above with regard to stability.However, it will evident to those skilled in the art that use of morethan one such membrane in series will give a still more uniform foam forgiven set of conditions.

It is believed that the combination of provision of a stream of solutionand gas under pressure through an aerosol valve and then flow throughthe passages, e.g. pores in a mesh, screen, membrane or sinter providesenergy sufficient to produce a stable aqueous liquid soluble gas, e.g.carbon dioxide and/or oxygen, based sclerosant foam that was previouslythought to be only producible by supply of high amounts of energy usinghigh speed brushes and blenders as described in the prior art.

A most preferred method of the invention provides a housing in which issituated a pressurisable chamber. For sterile supply purposes this willat least partly filled with a sterile and pyrogen free solution of thesclerosing agent in a physiologically acceptable aqueous solvent butotherwise may be charged with such at the point of use. This convenientmethod provides a pathway by which the solution may pass from thepressurisable chamber to exterior of the housing through an outlet andmore preferably a mechanism by which the pathway from the chamber to theexterior can be opened or closed such that, when the container ispressurized, fluid will be forced along the pathway and through one ormore outlet orifices.

The method is particularly characterized in that the housingincorporates one or more of (a) a pressurized source of thephysiologically acceptable gas that is readily dispersible in blood, and(b) an inlet for the admission of a source of said gas; the gas beingcontacted with the solution on activation of the mechanism.

The gas and solution are caused to pass along the pathway to theexterior of the housing through the one or more, preferably multiple,passages of defined dimension above, through which the solution and gasmust pass to reach the exterior, whereby on contact with, e.g. flowthrough, the passages the solution and gas form a foam.

Preferably the gas and liquid pass through a gas liquid interfacemechanism, typically being a junction between a passage and one or moreadjoining passages, and are converted to an aerosol, dispersion ofbubbles or macrofoam before passing through the passages, but asexplained they may be converted first to a macrofoam, e.g. by shaking ofthe device, e.g., by hand, or mechanical shaking device.

In another aspect of the present invention there is provided a devicefor producing a foam suitable for use in scleropathy of blood vessels,particularly veins, comprising a housing in which is situated apressurisable chamber containing a solution of the sclerosing agent in aphysiologically acceptable solvent referred to in the first aspect; apathway with one or more outlet orifices by which the solution may passfrom the pressurisable chamber to exterior of the device through saidone or more outlet orifices and a mechanism by which the pathway fromthe chamber to the exterior can be opened or closed such that, when thecontainer is pressurized and the pathway is open, fluid will be forcedalong the pathway and through the one or more outlet orifices:

said housing incorporating one or more of (a) a pressurized source ofphysiologically acceptable gas that is dispersible in blood and (b) aninlet for the admission of said gas; the gas being in contacted with thesolution on activation of the mechanism such as to produce a gassolution mixture,

said pathway to the exterior of the housing including one or moreelements defining one or more passages of cross sectional dimension,preferably diameter, 0.1 μm to 15 μm, through which the solution and gasmixture is passed to reach the exterior of the device, said passing ofsaid mixture through the passages forming a foam of from 0.07 to 0.19g/mL density and of half-life at least 2 minutes.

Preferably the apparatus includes a chamber, e.g. such as in a sealedcanister, charged with the blood dispersible gas and the sclerosantliquid, e.g. in a single chamber, the device pathway including a diptube with an inlet opening under the level of the liquid in this chamberwhen the device is positioned upright. Preferably the dip-tube has anoutlet opening at a gas liquid interface junction where the gas, whichresides in the chamber above the liquid, has access to the pathway tothe device outlet. The pathway is opened or closed by a valve elementwhich is depressed or tilted to open up a pathway to the exterior of thedevice, whereby the liquid rises up the dip tube under gas pressure andis mixed in the interface junction with that gas to produce an aerosol,dispersion of bubbles in liquid or macrofoam.

Either inside the pressurisable chamber disposed in the pathway to thevalve, or on the downstream side of the valve, is provided an elementhaving the one or more passages described in the first aspect mountedsuch that the gas liquid mixture, i.e. dispersion of bubbles in liquid,aerosol or macrofoam, passes through the passage or passages and iscaused to foam. This element may conveniently be located in a cap on thecanister in between the valve mounting and an outlet nozzle.Conveniently depression of the cap operates the valve. Alternatively theelement is within the canister mounted above the gas liquid interface.

In an alternate embodiment of this device the gas liquid interface maycomprise holes in the dip tube above the level of the liquid in thecanister inner chamber.

The gas pressure employed will be dependent upon materials being usedand their configuration, but conveniently will be 0.01 to 9 bar overatmospheric, more preferably 0.1-3 bar over atmospheric, and still morepreferably 1.5-1.7 bar over atmospheric pressure.

A preferred device of this aspect of the invention is of the‘bag-on-valve’ type. Such device includes a flexible gas and liquidtight container, forming a second inner chamber within the pressurisablechamber, which is sealed around the dip-tube and filled with the liquid.More preferably the dip-tube has a one-way valve located at a positionbetween its end located in the sclerosant liquid and the gas liquidinterface junction, which when the passage to the exterior is closed,remains closed such as to separate the liquid from the physiologicallyacceptable blood dispersible gas around it in the chamber. On openingthe pathway to the exterior, the one way valve also opens and releasesliquid up the dip-tube to the gas liquid interface where an aerosol isproduced which is in turn then passed through the passages to beconverted to foam. A suitable one-way valve is a duck-bill type valve,e.g. such as available from Vernay Labs Inc, Yellow Springs, Ohio, USA.Suitable bag-on-valve can constructions are available from CosterAerosols, Stevenage, UK and comprise an aluminum foil/plastics laminate.

Conveniently the one way valve is located at the top of the dip-tubebetween that and the gas liquid interface junction, i.e. an Ecosoldevice. This allows filling of the bag before application of the one wayvalve, followed by sterilization of the contents, whether in thecanister or otherwise.

Such a preferred device has several potential advantages. Where oxygenis the gas, this is kept separate from the liquid before use and thusreduces possibility of oxygen radicals reacting with organic componentsin the liquid, e.g. during sterilization processes such as irradiation.Where carbon dioxide is the gas, storage can lead to high volumes of gasdissolving in the liquid, which on release to the atmosphere or lowerpressure, could out-gas and start to destroy the foam too quickly. Suchseparation also prevents the deposition of solidified sclerosing agentcomponents in the dimension sensitive orifices of the device in anunused can in storage or transit, particularly should that be orientedother than upright.

It is preferred that the gas liquid interface is provided as a definedorifice size device such as the Ecosol device provided by PrecisionValve Peterborough UK. For a device where the passages of defineddimension are outside of the pressurized chamber, i.e. mounted on thevalve stem, the ratio of area of the gas holes to the liquid holesshould be of the order of 3 to 5, preferably about 4. Where the passagesare inside the pressurized chamber this is preferably higher.

Another aspect of the invention provides a device for producing a foamsuitable for use in sclerotherapy of blood vessels, particularly veins,comprising a housing in which is situated a pressurisable chamber, atleast part filled or fillable with a solution of a sclerosing agent in aphysiologically acceptable solvent and/or a physiologically acceptableblood dispersible gas; a pathway by which the contents of the chambermay be passed to exterior of the housing through one or more outletorifices and a mechanism by which the chamber can be pressurized suchthat its contents pass to the exterior along the pathway and through oneor more outlet orifices

-   -   said pathway to the exterior of the housing or the chamber        including one or more elements defining one or more passages of        cross sectional dimension, preferably diameter, 0.1 μm to 15 μm        through which the contents of the chamber may be passed, whereby        on passing through the passages the solution and gas form a foam        of from 0.07 to 0.19 g/mL density and having a half-life of at        least 2 minutes.

The elements defining the passages in the pathway or chamber may bestatic or may be moveable by manipulation of the device from outside ofits interior chamber.

Preferably the housing is a container defining a chamber in which issituated the solution and gas under pressure and the pathway is aconduit leading from the chamber in the interior of the container to avalve closing an opening in the container wall.

Preferred forms of the one or more elements defining the multiplepassages for use in the device of the present invention are meshes,screens or sinters. Thus one or more meshes or perforated screens orsinters will be provided, with some preferred forms employing a seriesof such elements arranged in parallel with their major surfacesperpendicular to the path of solution/gas expulsion.

It is preferred that all elements of any of the devices according to theinvention having a critical dimension are made of a material that doesnot change dimension when exposed to aqueous material. Thus elementswith such function such as the air liquid interface and the elementdefining the passages of 0.1 μm-15 μm dimension preferably should not beof a water swellable material such as Nylon 66 where they are likely tobe exposed to the solution for more than a few minutes. Where suchexposure is likely these parts are more preferably being fashioned froma polyolefin such as polypropylene or polyethylene.

Preferably the canister is sized such that it contains sufficient gasand solution to form up to 500 mL of foam, more preferably from 1 mL upto 200 mL and most preferably from 10 to 60 mL of foam. Particularly theamount of gas under pressure in such canisters should be sufficient toproduce enough foam to treat, i.e. fill, at least one varicosed humansaphenous vein. Thus preferred canisters of the invention may be smallerthan those currently used for supply of domestic used mousse type foams.The most preferred canister device is disposable after use, or cannot bereused once opened such as to avoid problems of maintaining sterility.

It may be preferred to incorporate a device which maintains gas pressurein the canister as foam is expelled. Suitable devices are such asdescribed under trademarked devices PECAP and Atmosol. However, where asignificant headspace or pressure of gas is provided this will not benecessary.

The canister system has some drawbacks, however. It is relativelycomplex and thus expensive. Furthermore, the initial quantity of foamgenerated using a canister system can be of unpredictable quality andthus tends to be diverted off to waste prior dispensing foam for use. Itis not easy to deliver foam direct from a pressurized canister into acannula in a patient's vein; although this is theoretically possible, itwould require special valve/control arrangements on the canister outputto allow for the delivery rate to be highly controllable by theclinician administering the treatment. A further issue is that, wheneverdispensing of foam is stopped or slowed significantly, it is necessaryon re-starting to divert a quantity of foam to waste again beforedispensing usable foam.

For all these reasons, the canister product mentioned above, though awell designed and highly effective system, is designed to deliver foamproduct into a syringe for subsequent administration to a patient. Aspecial foam transfer unit is used for this purpose. The syringe nozzleis inserted into a port on this transfer device and the device is thenused to divert the first portion of foam before charging the syringewith usable foam.

A further issue is that the foam, once made, immediately starts tochange—liquid drains out and bubbles coalesce. A period of time isrequired time for the clinician to divert an initial quantity of foamfrom a canister, charge a syringe with good foam, connect it to a lineto a patient's vein and administer the foam. This time will vary withdifferent clinicians and even the same clinician will not always takethe same length of time. Furthermore, each treatment is different andthe foam will be injected over a different period; sometimes theclinician will stop dispensing foam for a short period and thenrecommence. All this time, the properties of the foam will be changing.

There are other techniques for generating foam for use in sclerotherapy,including the so called “Tessari” and “DSS” techniques, each of whichinvolves pumping liquid sclerosant and gas between two syringes. Thesetwo techniques are widely used for generating sclerosing foams made withair, and there are also a number of other less widely used techniques.Although these techniques are simpler than a canister system, they offerno solutions to the problems mentioned above and they also have theirown problems such as unpredictability of the product and the difficultyin using any gas other than ambient air.

The inventors realized that it would be desirable to have a device whichcould be connected directly to the patient and would generate foam as itwas needed, so that the foam had the minimum possible time to degradebefore entering a patient's vein. Ideally the device would also not havethe problem of producing an initial quantity of poor foam. The deviceshould be suitable for containing a gas other than air for incorporationinto the foam.

The inventors also realized that, particularly for a highly soluble gas,the device should ideally not store the gas together with the liquidunder a pressure substantially greater than atmospheric. With a solublegas, especially a highly soluble gas such as carbon dioxide, storing thegas and liquid under pressure can contribute to the speed of decay ofthe foam. This is because the pressurized gas tends to go into solutionin the sclerosant liquid. On exit of the foam, the gas comes out ofsolution into the bubbles thereby accelerating degradation of the foam.Pressurizing the gas also, of course, adds to the complexity and expenseof the system.

According to a first aspect of the invention, a device for generatingand dispensing foam for therapeutic use comprises:

-   -   (a) a housing;    -   (b) the housing having a first chamber of adjustable volume        containing gas at substantially atmospheric pressure;    -   (c) the housing further having a second chamber of adjustable        volume containing sclerosant solution;    -   (d) an outlet for dispensing the liquid and sclerosant solution        in the form of a foam and a flow path communicating between the        outlet and the said first and second chambers;    -   (e) the flow path including a region in which mixing of the gas        and solution takes place;    -   (f) a foaming unit located downstream of the mixing region, the        foaming unit having holes with a dimension transverse to the        flow direction of between 0.1 and 100 micron.

It is preferred that the hole dimension be from 1 to 50 micron, morepreferably 2 to 20 micron, still more preferably 3 to 10 micron. Theseholes may be provided by a mesh, perforated screen, sinter or fabric,for example. Although the shape and orientation of the holes may not beregular, the unit should have a major proportion (greater than 50%,preferably greater than 80%) of holes where at least one dimension in adirection approximately transverse to the flow should be in the rangesspecified above.

In use, the volumes of the first and second chamber are adjusted inorder to drive the gas and solution out of the chambers and through themixing region and foaming unit. A mixture of gas and solution is formedas the gas and liquid pass through the mixing region and then a foam isformed as the mixture passes through the foaming unit.

It is preferable for the liquid and gas to be driven through the mixingregion and foaming unit at a flow rate which falls within apredetermined range, the desired flow rate range depending on thecharacteristics of the liquid and of the gas, the characteristics of themixing region and foaming unit, and possibly other characteristics ofthe system. The volume of the chambers may be varied manually to createthe foam, but it is preferred that the adjustment of the chambers becarried out using some other source of motive power, e.g. an electric,clockwork, pneumatic or hydraulic motor or by the direct action ofpressurized gas or even a simple spring. An on/off control is preferablyprovided for the user to commence and to stop delivery of foam.

The source of motive power may be provided as part of the device.Alternatively, the device may be designed as a cartridge for insertioninto a delivery device which may for example be similar to known devicesfor automatically delivering medication from a syringe over an extendedperiod of time.

The device may be configured with a flexible housing in form of e.g. abag with dual chambers, or two separate bags, connected to a mixingregion and foaming unit. The bag or bags may then be rolled up in adelivery device or the contents squeezed out by some other mechanicalmeans. Desirably, the chambers are of a size and shape which allow themto be squeezed out at the same rate, in terms of velocity, to achieve adesired foam density. This allows the mechanical means for squeezing thechambers to be of a more simple design.

Alternatively the device may be configured as a syringe, with the firstand second chambers having respective plungers which may be depressed inorder to expel the contents. Preferably size and shape of the chambers,most notably their cross sectional areas, are selected so that theplungers may be driven at the same speed to achieve a desired ratio ofgas to liquid in the foam.

As discussed above, the device may be suitable for connection to acannula needle, optionally via a line, for delivery of foam into thebody, e.g. into a vessel such as a blood vessel, especially a varicosevein or other venous malformation. Since the foam is generated by thesame action which expels the foam from the outlet, it may be possible toconnect the cannula to the outlet of the device and administer foam to apatient at the same time as generating it. This is clearly a muchsimpler procedure than generating the foam, drawing it up into asyringe, connecting the syringe to a line/cannula and then administeringthe foam.

According to the invention, a method for administering a foam to thehuman body, e.g. into a vessel such as a blood vessel, especially avaricose vein or other venous malformation, comprises the steps of: (a)sclerosant foam generating device to a cannula needle inserted into apatient; and (b) operating the device to generate and dispense foam tothe patient. Specifically, the steps may include:

-   -   (a) connecting a device as described above to a cannula needle        inserted into a patient;    -   (b) adjusting the volume of the said first and second chambers        so as to generate and deliver foam to the patient.

A further advantage of the generation and delivery of the foam in asingle step is that the foam has very little time to degrade prior toentering the body to perform its function, e.g. the sclerosis of avaricose vein. The device is therefore particularly suitable forgenerating foams with very soluble gases, such as carbon dioxide ornitrous oxide, which tend to revert to their gaseous and liquid phasesrelatively quickly.

Since the gas and liquid are stored in separate chambers until formationof the foam, there is very little possibility for the gas to becomedissolved in the liquid, which tends to happen with the pressurizedcanister systems described in the prior art.

According to the invention, a foam is provided which is made with asclerosant solution, e.g. polidocanol solution, and a gas, wherein, oncreation of the foam, the dissolved level of the gas in the solution isnot substantially higher than that of the solution when exposed toatmosphere at s.t.p., and wherein the gas is at least 70% by volumecarbon dioxide, more preferably at least 90% carbon dioxide, still morepreferably substantially 100% carbon dioxide. The gas may also include0.1 to 50% oxygen. Alternatively the gas may be substantially 100%nitrous oxide or a mixture of nitrous oxide and carbon dioxide.

Also according to the invention, a device is provided for generatingfoam from a sclerosant liquid, e.g. polidocanol solution, and a solublegas as described above, wherein the device incorporates a chamber inwhich the gas is stored at substantially atmospheric pressure.Preferably, the device further comprises a chamber in which sclerosantliquid is stored. Preferably, the device further includes a foaming unitfor creating a foam from the gas and sclerosant liquid, the foaming unithaving holes with a dimension transverse to the flow direction ofbetween 0.1 and 100 micron, such as 1 to 50, 2 to 20, 3 to 11, andespecially about 5.

Further features and advantages of the invention will be apparent fromthe following description of various specific embodiments, which is madewith reference to the accompanying drawings.

One embodiment of a device according to the invention comprises asyringe type device comprising a syringe barrel having an annularchamber containing gas and a central chamber for receiving a cartridgeof sclerosant solution, e.g. 1% polidocanol solution. FIG. 1 shows asyringe barrel 1 in a storage condition with its open ends closed withseals 2 of metal/plastic laminate material. The barrel 1 comprises anouter cylindrical wall 3 having a conical tapered end portion 4 at thefront, from which extends a standard luer nozzle 5. Disposed within theouter cylindrical wall is an inner cylindrical wall 6 defining an innerchamber 14. The front of the inner wall 6 is partly closed by and endface 8, in which is formed an orifice 9 with a frangible seal 10. Theinner wall is supported at the front end by a web 11, in which apertures12 are formed.

The outer and inner walls 3, 6 define between them an annular space 7which is filled with substantially 100% pure carbon dioxide gas. Theannular space 7 communicates with the interior space of the luer nozzle5 via the apertures 12 in the web 11. Located at the rear of the barrel,in the annular space 7, is an annular plunger seal 13 of resilientplastics material which seals against the outer and inner cylindricalwalls 3, 6.

FIG. 2 shows a cartridge comprising a glass tube 20 filled with 1%polidocanol and sealed at each end by a resilient plastics bung 21. Oneor both of the bungs may function as a plunger seal, that is to say itmay be movable down the length of the tube whilst retaining a sealingcontain with the interior wall of the tube. The cartridge of FIG. 2 isnot suitable for use with the syringe barrel described above, but couldbe used with a modified version of the barrel as discussed below.

FIG. 3 shows a cartridge suitable for use with the syringe barreldescribed above with reference to FIG. 1. The cartridge comprises aglass tube 30 which is filled with 1% polidocanol solution. At the rearend of the tube 30 is a resilient bung 31 which is capable offunctioning as a plunger seal as described above. At the front end ofthe tube is an end face 32 in which is located a nozzle 33, sealed withan end cap 34. The size and shape of the tube 30 complements the shapeof the inner wall 6 of the syringe barrel of FIG. 1. In particular, thediameter of the tube 30 is such that the tube is a close fit in theinterior space 14 defined within the inner wall 6 of the barrel 1, andthe nozzle 33 of the cartridge is sized so that, when fully insertedinto the interior chamber 14 of the barrel, it protrudes through theorifice 9 in the front of the chamber 14 (the end cap 34 having firstbeen removed).

Cartridges of the type shown in FIGS. 2 and 3 are well known for liquiddrugs. The cartridges are fitted to specially designed injection devicesto administer the drug, and the empty cartridge then removed from thedevice and disposed of.

FIG. 4 shows a cartridge 30 as shown in FIG. 3 being inserted into thebarrel of FIG. 1. Note that the end cap 34 of the cartridge has beenremoved.

FIG. 5 shows the cartridge 30 fully inserted into the barrel 1 such thatthe nozzle 32 seals in the orifice 9 of the interior chamber 14 of thebarrel. A syringe plunger stem 40 is fitted to the rear of the syringebarrel 1. The plunger stem 40 comprises a disc 43 for applying manualpressure, connected via shafts 44 to a central disc shaped pressure pad41 and an annular pressure pad 42. The pressure pads 41, 42 are engagedwith bungs/plunger seals 31, 13, respectively, of the annular barrelchamber 7 and of the cartridge 30.

At the front of the barrel 1, a foaming unit 50 is fitted to the luernozzle 5. The foaming unit comprises a stack of mesh elements withmicroscopic perforations. The foaming unit will be described in moredetail below in relation to FIGS. 11, 12 and 13.

In use, the plunger stem 40 is depressed either manually or in a syringedriver such as the one shown schematically in FIG. 8 and discussedbelow. The syringe with partly depressed plunger stem and foaming unitfitted is shown in FIG. 6. The plunger seals 13, 31 in the annularcarbon dioxide chamber and in the chamber defined within the cartridgeare advanced as the plunger stem is depressed, thereby driving carbondioxide and polidocanol solution through the apertures 12 and theorifice 9. Mixing of the gas and liquid takes place in the region 15 infront of the orifice 9 where the annular gas flow interacts with theliquid flow. The mixture then proceeds as indicated by arrow A in FIG. 6through the syringe nozzle 5 into the foaming unit 50 where the gas andliquid are passed through microscopic perforations of average dimension5 micron to create a fine foam or foam with an average bubble size ofaround 100 micron.

FIG. 7 shows an alternative syringe-based design. A syringe barrel 101houses twin parallel gas and liquid chambers 107, 114 which receiverespective cartridges 170, 120 of the type shown in FIG. 2 withresilient bungs 171 a, 171 b, 121 a, 121 b at each end. The gas chamber107 contains cartridge 170 which is filled with substantially 100% purecarbon dioxide at substantially atmospheric pressure. The liquid chamber114 contains cartridge 120 which is filled with 1% polidocanol solution.

At the rear end of the barrel 101 a plunger stem is fitted, comprising adisc 143 for applying manual pressure, connected via shafts 144 to twodisc shaped pressure pads 41, 42 received within the gas and liquidchambers 107, 114 respectively.

At the front end of the syringe barrel is an end wall 104 from whichprojects a cylindrical hub 116 with a nozzle 105 at the end. Within thehub 116 is a mixing chamber or mixing region 115. In this region arelocated static mixing fins 117. Located at the front of the chambers107, 114 are hollow needle-like members 118, 119 respectively, each witha point 118 a, 119 a facing into the respective chamber. Eachneedle-like member is contoured to lie along the front face of itsrespective chamber and to extend into the mixing chamber 115.

Fitted to the nozzle 105 of the syringe is a foaming unit 50 of similardesign to that used in the device of FIGS. 1 to 6. The foaming unit willbe described more fully below with reference to FIGS. 11-13.

The syringe is supplied with cartridges 120, 170 pre-fitted. A clip 119prevents depression of the plunger stem 140 until the clip is removedimmediately prior to use. When it is desired to use the syringe, theclip 119 is removed and the plunger manually depressed so that thecartridges 120, 170, which are a snug fit in their respective chambers114, 107, are advanced into contact with the needle elements 119, 118respectively. Further depression of the plunger stem 140 causes theneedle points 119 a, 118 a to penetrate the resilient bungs 121 a, 171 aat the front of the cartridges, thereby opening a communication channelbetween the interior of the cartridges and the mixing chamber 115.

Further depression of the plunger stem 140 causes carbon dioxide andpolidocanol solution to flow together into the mixing chamber, in aratio predetermined by the cross-sectional areas of the cartridges. Fins117 in the mixing chamber ensure that the gas and liquid are thoroughlymixed prior to entering the foaming unit 50 where the liquid and gas isconverted into a foam.

When treating a patient, the clinician would go through the above stepsand ensure that consistent foam is being discharged from the foamingunit 50. Pressure is then released from the plunger stem 140 and a linefrom a cannula, which has previously been inserted into a vein to betreated, is connected by a standard luer fitting to the exit of thefoaming unit. Pressure would then be applied again to the plunger stem140 to produce foam and at the same time inject it through the line andcannula and into the patient's vein.

The exact properties of the foam will depend to some extent on the speedat which the plunger stem 140 is depressed. For this reason it ispreferable that a syringe driver is used to administer the foam. Asyringe driver is shown schematically in FIG. 8, with the syringe ofFIG. 7 fitted in it. The driver 200 comprises a base 201, syringe clamp202 and motor 204 fitted in a motor mounting 203. The motor 204 iscoupled via a coupling 209 to a drive shaft 206 having an externalthread 210. Received on the drive shaft is annular member 207 having aninternal thread 211 engaged with the external thread 210 of the driveshaft. From the annular member 207 extends a driving member which bearson the plunger stem 140 of the syringe which is clamped in the syringeclamp 202.

The motor is connected to a DC power supply 212, has a speed calibrationcontrol 209 for setting the correct drive speed, and also an on/offcontrol 205.

In use, the clinician would remove the clip 119 from the syringe of FIG.7, depress the plunger stem 140 to the point where consistent foam isbeing produced, then insert the syringe into the driver and connect upto a line 80 previously installed in a patient's vein. The speed of themotor 204 would previously have been calibrated to a speed appropriatefor the syringe being used. The clinician then has control of thedelivery of foam to the patient by means of the on/off switch.

As short a line as possible is used, so that a very small quantity offoam resides in the line when the motor is switched off. In this way, itis ensured that almost all the foam delivered to the patient has beengenerated only a few moments previously and has had very littleopportunity to degrade.

FIGS. 9 and 10 show an alternative embodiment 300 of foam generating anddispensing device. This embodiment is based on a bag 301 ofmetal/plastics laminate material. In the bag are located chambers 302,303 separated by ultrasonically welded seams 310. The chambers 302, 303contain carbon dioxide and 1% polidocanol solution respectively. Thechambers are disposed in parallel along substantially the whole lengthof the bag, and the cross sections of the chambers, when filled, isselected so as to ensure a correct gas/air mix as with the syringeembodiments. Each chamber 302, 303 has a channel 304, 305 leading to amixing region or mixing chamber 306 defined within a housing 307. On thefront of the housing 307 is a luer nozzle 308, to which is fitted afoaming unit 50 as with previous embodiments. Within the mixing chamber306 are located mixing fins 311.

At the rear of the bag 301 is a relatively stiff rod 309. In use, thebag 301 is rolled around the rod 309 to expel gas and liquid from thechambers 302, 303 respectively. As with previous embodiments, the gasand liquid enter the mixing chamber where they are well mixed beforeentering the foaming unit 50 and being converted to foam of presetdensity.

As with the other embodiments, the bag is preferably used with a driverdevice such as is shown schematically in FIG. 10. In FIG. 10 the bag 301can be seen in side view, held in place on a movable carriage 321,slidably mounted on a base plate 320. The rear of the bag 301 is clampedby a bag clamp 322 at the rear of the carriage 321; the rod 309 in thissituation serves to help prevent the bag slipping through the clamp. Themixing chamber housing 307 at the front of the bag is clamped in amixing chamber clamp 323 at the front of the carriage 321.

To set up the driver, the carriage, complete with bag, is slid sidewaysunder a roller 324 mounted on the base plate 320. In order to do this,the bag is manually depressed at the rear end, adjacent the rod 309 toallow it to fit under the roller 324.

The roller 324 is driven by an electric motor 325 supplied from a DCpower supply 326. The speed of the motor may be calibrated using speedcontrol 327 and stopped and started using on/off switch 328.

On starting the motor, the roller rotates in the sense indicated byarrow B, causing the carriage, complete with bag, to slide under theroller. Gas and liquid contained in the bag is thereby forced throughthe mixing chamber 306 and foaming unit 50, and out of an exit of thefoaming unit.

As with the previous embodiments, the clinician would ensure thatconsistent foam is being produced before connecting up a line 80 to acannula installed in a patient's vein.

Referring now to FIGS. 11 to 13, the foaming unit comprises four meshelements, each comprising a ring 51 having a mesh 52 secured across it.The mesh has perforations of diameter approximately 5 micron. Each meshelement has male and female sealing surfaces 53, 54 respectively—theseare best seen in FIG. 12.

FIG. 13 shows four mesh elements stacked together such that the malesealing surface of one element engages the female surface of the elementnext to it. The elements are retained in housing 55 having a socket half56 and a nozzle half 57. Between these halves of the housing, the meshelements are retained under pressure, with the sealing surfaces 53, 54engaging with each other and with the interior of the housing 55 at eachend. In this way a good seal is created between the mesh elements, sothat all flow through the foaming unit must pass through the mesh.

The socket end 56 of the housing is formed with a standard luer socket58 which, in use, fits over the luer nozzle output of the variousdevices described above. The nozzle end 57 of the housing incorporates astandard luer nozzle 59 onto which a medical line having a standard luersocket may be fitted.

Alternatives to the mesh elements described are contemplated: anythingwhich provides pores, perforations, interstices, etc. with a dimensionin a direction approximately transverse to the direction of flow ofbetween 0.1 micron and 100 micron may be suitable. Examples mightinclude a fabric, perforated screen or sinter.

The following examples are provided in support of the inventive conceptsdescribed herein.

The present invention will now be described further by way ofillustration only by reference to the following Figures and Examples.Further embodiments falling within the scope of the invention will occurto those skilled in the art in the light of these.

EXAMPLE 1

10 patients were treated for varicose veins by injection of foam madewith 1% polidocanol solution and a gas mix consisting essentially of7-8% nitrogen and the remainder carbon dioxide (about 22%) and oxygen(about 70%).

The procedure involved the injection of up to 30 ml of foam (25.5 mlgas) into the thigh section of the greater saphenous vein. 4-chambercardiac ultrasound examinations were conducted on all the patients totest for bubbles reaching the heart. Bubbles were observed in the rightatria and ventricles of all 10 patients examined. In general, bubblesappeared several minutes following injection of the foam and continueduntil the ultrasound recording was stopped about 40 minutes afterinjection.

In one patient, microbubbles were observed in the left atrium andventricle. This patient was subsequently confirmed to have a patentforamen ovale.

EXAMPLE 2

The objective of this experiment was to investigate the nature of theresidual bubbles that pass into the heart following injection into thesaphenous vein of polidocanol foam made with different gas mixtures.

An anesthetized female hound dog weighing 26 kg was injected with foamcontaining polidocanol formulated with varying gas mixes. Residualbubbles were monitored in the pulmonary artery using transoesophagealechocardiogram (TEE). Residual bubbles visualized on TEE were sampledfrom the pulmonary artery through a wide-bore catheter. These bloodsamples were analyzed for the presence of residual bubbles using lightmicroscopy and ultrasound.

Three different compositions of foam were used, as follows:

1% polidocanol and air

1% polidocanol and a gas mix consisting of 7-8% nitrogen and theremainder carbon dioxide and oxygen

1% polidocanol solution and a gas mix comprising less than 1% nitrogenand the remainder carbon dioxide and oxygen.

The TEE output was videotaped and subsequently analyzed. For all threecompositions, bubbles reached the pulmonary artery in sufficientquantity to cause a substantially opaque image. It is believed that thethreshold bubble density required to produce such an image as quite low,and therefore this image in itself did not provide useful data. The timetaken for the occluded image to revert to a steady state backgroundimage was believed to be approximately indicative of the length of timetaken for all or most the bubbles to have dissolved into thebloodstream. The TEE was very sensitive (showing activity even whensaline was injected as a control); for this reason exact end points weredifficult to determine. However, the following estimates have been madeof the time period from opacification of the image to decay down to abackground level.

4 minutes

2 minutes

20 seconds.

In addition to the TEE analysis, observations were made of samples ofblood drawn from the pulmonary artery for each foam during the periodwhen the TEE image was substantially opaque. The results of theseobservations were as follows.

As soon as the sample was taken, a considerable volume of bubbles wasobserved in the syringe. When the syringe was held with its longitudinalaxis horizontal, a continuous strip of bubbles was observed extendingsubstantially the full length of the 20 ml syringe.

Initially on taking the sample no bubbles were observed in the syringe,but after a few seconds, with the syringe in the horizontal position, aline of bubbles appeared which was thinner than the line observed forfoam A.

After taking the sample and holding the syringe in the horizontalposition, no bubbles were observed for a period of a minute or more.Gradually, a thin line of bubbles began to appear along the top of thesyringe.

It was not possible to measure the bubbles, but they appeared to besmaller for composition C than for composition B, with the bubbles fromcomposition B in turn smaller than those from composition A.

EXAMPLE 3

In vitro experiments were conducted to determine the absorption of foammade with different gases in fresh human venous blood.

A 20 ml polypropylene syringe barrel was prepared by puncturing its sidewall with a relatively large hypodermic needle to make a holeapproximately 1 mm in diameter. This hole was then covered by securing apiece of clear flexible vinyl sheet over it with clear adhesive tape. Asmall magnetic stirrer element was introduced into the syringe barreland the plunger then replaced. 20 ml of human venous blood was then withwithdrawn in the usual manner from a human subject using the speciallyprepared syringe fitted with a hypodermic needle.

The hypodermic needle was removed and the syringe then placed on amagnetic stirrer unit so that the magnetic element in the syringethoroughly agitated the blood. The Luer nozzle of the syringe was thenconnected to a 50 cm piece of manometer tubing which was arrangedhorizontally and left open at one end. The manometer tubing was securedagainst a scale.

A 0.5 ml measuring syringe with a fine pre-fitted needle was then filledwith foam made from 1% polidocanol solution and air. The density of thefoam was 0.13 g/ml (±0.03 g/ml), the liquid component making upapproximately 13% of the total volume of foam (±3%).

The needle of the 0.5 ml syringe was then introduced through the vinylsheet on the side wall of the 20 ml syringe. A small volume of blood wasfound to have entered the manometer tubing and the position of thedistal end of this column of blood was noted against the scale. The 0.5ml aliquot of foam was then injected quickly and simultaneously a timerstarted (t0). As the foam displaced blood in the 20 ml syringe, thecolumn of blood from the 20 ml syringe was displaced into the manometertubing and the distance along the tubing reached by the distal end ofthe blood column was noted against the scale. The scale itself comprisedspaced marker lines equally spaced at about 1 cm intervals. It wasdetermined that a distance of 45 intervals on this scale corresponded toan internal volume of in the manometer tubing of approximately 0.5 ml.

As the gas in the foam started to be absorbed by the blood, the blood inthe manometer tubing started to recede back towards the syringe. Afterthe column appeared to have stopped moving, the timer was stopped (tF).The position of the distal end was again noted.

This experiment was then repeated for a foam of the same density butmade with oxygen gas (“medical grade” purity—99.5% minimum).

The experiment was repeated again but this time oxygen gas from acylinder of medical grade oxygen was introduced directly into the 0.5 mlsyringe instead of foam.

The results of these three tests ate presented below in Table 1. TABLE 1Start Position Position Absorbed Liquid position of blood of bloodvolume at Volume Unabsorbed of blood at t₀ t_(F) at t_(F) t_(F) (ml) infoam gas Test Foam/gas (“x”) (“y”) (seconds) (“z”)$\frac{0.5\quad( {y - z} )}{( {y - x} )}$ (ml) ml% 1 Air 2 47  80* 40 0.08 0.13 × 0.35 81% foam 0.5 = 0.07 2 Oxygen 4 48140  11 0.42 0.13 × 0.01  2% foam 0.5 = 0.07 3 Oxygen 2 47 140  5.5 0.46nil 0.04  8%*No further movement of the blood column was observed after 80 seconds.

The experimental error in this example is unfortunately too great toconclude whether there is or is not a residual volume of gas for theoxygen gas or oxygen foam, although clearly the great majority at leastof the gas is absorbed. There will have been a small percentage ofnitrogen in the gas, from the oxygen cylinder which is only 99.5% pure,and possibly also introduced during the experiment. Diffusion ofnitrogen into the bubbles from the blood is also a possibility, asdiscussed above, and some nitrogen may have been introducedinadvertently during the procedure.

In this experiment, the air foam test was only observed for a fewminutes after tF. However, further experiments have been conducted bythe inventors, the results of which are not formally recorded here,involving foam with a percentage of nitrogen. A 20 ml syringe of freshhuman venous blood, as in the above experiments, was injected with a 0.5ml aliquot of a foam containing a percentage of nitrogen. The contentsof the syringe were agitated as above and a period of 24 hours allowedto elapse. An easily visible volume of bubbles remained in the syringe.

EXAMPLE 4 Preparation of Ultra-Low Nitrogen Canister

An anodized aluminum canister with an open top was filled with water.The canister was then immersed in a bath of water and inverted. A linefrom a pressurized cylinder of oxygen gas was then introduced into thewater bath and the supply of oxygen turned on, thereby flushing the lineof any air. A canister head assembly comprising a valve, dip tube andmesh stack unit was then immersed in the water bath and connected to theoxygen line for a few seconds to purge air from the assembly.

The oxygen line was then introduced into the inverted canister until allwater had been displaced from the canister. The line was then removedfrom the canister and the previously purged head assembly quicklyclamped over the top of the canister thereby sealing the canister. Thecanister was then removed from the water bath with the head assemblystill clamped against it; the head assembly was then secured to thecanister using a standard crimping technique.

The canister was then pressurized to about 8 bar absolute pressure byconnecting the canister valve to a regulated oxygen line for 1 minute.The pressure as then relieved by opening the valve until the pressure inthe canister was just above 1 bar absolute; a pressure gauge was appliedto the valve intermittently during the pressure release operation toensure that the canister pressure did not drop all the way down to 1 barabsolute. This was done to avoid the possibility of atmospheric airseeping into the canister.

The canister was then pressurized again up to about 8 bar absolute andthe pressure release operation repeated. This process was then repeateda third time, with the final canister pressure being from 1.1 to 1.2 barabsolute.

18 ml 1% polidocanol solution was then introduced through the canistervalve using a syringe with all air pockets, including any air in theluer nozzle, removed. The canister valve was then connected to a carbondioxide cylinder and pressurized to 2.2 bar absolute. Then the oxygenline was again connected to the valve and the pressure increased to 3.6bar absolute.

Table 2 below shows the expected result from the oxygen pressurizing anddepressurising cycles, assuming 100% pure oxygen in the cylinder andassuming that despite the precautions taken 1% of the gas in thecanister after the initial oxygen filling procedure is nitrogen. Theworst case is assumed for the canister pressure values, namely 1.2 barabsolute (“bara”) and 7.6 bara. TABLE 2 N2 partial Canister pressurepressure (bara) (bara) % N2 Start 0.012 1.2   1% 1^(st) cycle 0.012 7.60.16% 0.00189 1.2 0.16% 2^(nd) cycle 0.00189 7.6 0.02% 0.000299 1.20.02% 3^(rd) cycle 0.000299 7.6 0.00% 0.0000472 1.2 0.00%

As can be seen the percentage of nitrogen drops down to zero, calculatedto two decimal places, after the three oxygen pressure/release cycles.

The oxygen cylinder used in the above process was a standard medicalgrade oxygen cylinder supplied by B.O.C. and specified at 99.5% orgreater purity. The carbon dioxide cylinder used was so called “CPGrade” from B.O.C. which has a purity level of 99.995%.

Working to two decimal places, the impurity (which will be mainlynitrogen) arising from the initial filling procedure should be reducedto zero after three pressure/release cycles. Similarly the impuritylevel in the canister from the carbon dioxide cylinder can be consideredzero to two decimal places, since the purity of the source was 99.995%and only approximately one third of the gas in the finished canister wascarbon dioxide.

The inventors will perform further experiments along the above linesusing oxygen and carbon dioxide sources of higher purity. The followingcylinder oxygen is readily available from B.O.C.:

“Medical grade” 99.5% purity (as used in the above procedure)

“Zero grade” 99.6% purity

“N5.0 grade” 99.999% purity

“N5.5 grade” 99.9995% purity

“N6.0 grade” 99.9999% purity

In each case the impurity is mainly nitrogen.

The following cylinder carbon dioxide products are readily availablefrom B.O.C. They have the following specifications:

“C.P grade N4.5” 99.995% purity (as used in the above procedure)

“Research grade N5.0” 99.999% purity.

It will be appreciated that repeating the procedure described aboveusing “Zero grade” oxygen would result in a finished canister havingmaximum impurity (which will be mainly nitrogen) of 0.4%.

Of course the number of pressure/release cycles may be increased inorder further to reduce the theoretical maximum impurity if the oxygenand carbon dioxide sources were 100% pure. It is a simple calculation toshow the number of cycles necessary to reduce the maximum percentageimpurity level to zero, calculated to 3, 4 or 5 decimal places. Providedthe canister pressure never drops to or below 1 bar absolute andprovided the lines from the oxygen and carbon dioxide cylinders areflushed through with gas prior to attachment to the canister valve,there is no reason to assume that any significant impurity will enterthe canister during the pressure/release cycles.

A refinement of the procedure to reduce further any opportunity forimpurity to enter would be to introduce the polidocanol solutionimmediately after initial flushing. In this way, any air/nitrogenintroduced with the polidocanol will be eliminated during the subsequentpressure/release cycles.

A further refinement of the technique might be to maintain the waterbath in an agitated state using a magnetic stirrer, under a continuouslyrefreshed oxygen atmosphere for 24 hours. In this way, any dissolvednitrogen in the water bath should be eliminated and replaced withdissolved oxygen. Filling the canister from this oxygenated water bathshould, it is postulated, remove the water bath as a possible source ofnitrogen impurity.

It is envisaged that five, ten, twenty or even 100 pressure/releasecycles could be performed.

In this manner, using appropriate sources of oxygen and carbon dioxideas detailed above, it will be possible to make a canister charged withpolidocanol and an oxygen and carbon dioxide mix having a percentageimpurity of 0.005% or less (mainly nitrogen) using CP grade carbondioxide or 0.001% or less using research grade carbon dioxide. It shouldalso be possible to make a polidocanol and oxygen canister with apercentage impurity of nitrogen gas of 0.0001% or less using N6.0 gradeoxygen.

It will of course be appreciated that the production of canisters inthis way having a somewhat higher minimum nitrogen level is notdifficult and may be achieved, for example, by reducing the number ofpressure/release cycles.

It will also of course be appreciated that substitution of polidocanolby an alternative liquid component would be a trivial matter.

EXAMPLE 5 Preparation of Ultra-Low Nitrogen Canister

The inventors are at present developing a procedure for large scalemanufacture of ultra-low nitrogen canisters, using a similarmethodology. In this procedure, two canisters are manufactured, onecontaining oxygen at 5.8 bar absolute and the other carbon dioxide andpolidocanol solution at about 1.2 bar absolute. In use, theCO2/polidocanol canister is pressurized immediately prior to use byconnecting it to the oxygen canister. This is described inWO02/41872-A1[CDE10].

There is therefore a separate manufacturing procedure for the oxygen andcarbon dioxide/polidocanol canisters. However, it will be apparent thateither procedure is applicable to production of a single canisterproduct containing polidocanol and oxygen, carbon dioxide or a mix ofthe two.

The procedure will be described first for an oxygen canister, which issimply an anodized aluminum canister with a standard valve assembly inthe top. Prior to fitting the valve assembly, the canister is firstflushed with oxygen gas by inserting an oxygen line into the open top ofan upright cylinder for 10 seconds. The line is then withdrawn. At thisstage not all the air will have been eliminated and it is believed thatthe nitrogen impurity level is around 5% or 6%; this has not beenmeasured specifically, but has been deduced from the measured impuritylevel at a later stage in the procedure (see below). It is not believedthat flushing the canister for a longer period would substantiallychange this value for nitrogen gas impurity.

The valve assembly is then loosely fitted and a filling head broughtinto engagement around the top of the canister and valve assembly so asto make a gas-ight seal against the canister wall. Connected to thefilling head is a line for oxygen. The canister is then brought up to apressure of approximately 5.5 bar absolute (bara). Nitrogen gas impurityat this stage has been measured by standard gas chromatographytechniques to be about 1%.

At one stage it was thought to be acceptable to have the nitrogenimpurity level at around 1%, but following the results of the clinicaltrial (Example 1), it has been determined that a lower nitrogen contentis desirable. For this reason, further steps have been added to theprocedure, as follows.

Maintaining the seal between the canister and filling head, the contentsof the canister are exhausted via the filling head until the pressure inthe canister is just over 1 bara. As with Example 4 above, this is toprevent any potential ingress of atmospheric air through the seal.

Maintaining the seal between the canister and filling head, the pressureis then increased again to about 5.5 bara and again this pressure isreleased down to just over 1 bara. The canister is then brought up toits final pressure of 5.5 bara±0.4 bara. At this stage, the nitrogen gasimpurity measured by gas chromatography is about 0.2%.

It will be appreciated that each of the pressure/release cycles shouldreduce the impurity due to residual air/nitrogen by a factor of about 5assuming no leakage. It is reasonable to assume no leakage since apositive pressure is always maintained in the canister. Assuming a 100%pure source of oxygen, the theoretical nitrogen impurity after thesethree pressure/release cycles should be around 0.05%. Since the measurednitrogen level is around 0.2%, there is apparently either impurity inthe line or nitrogen is entering the sample during the measuringprocess. It can at least be concluded that the impurity level is 0.2% orbetter.

It will be appreciated that polidocanol solution, or any other liquidsclerosing agent, could be added into the canister during the aboveprocedure and the standard valve and dip tube could be replaced with aunit including foam generating means such as a small aperture mesh. Inthe final step, the pressure in the canister may be brought up towhatever is required, e.g. around 3.5 bara. In this way, a finalpressurized canister product containing sclerosant and substantiallypure oxygen could be made.

At present, the effects, including possible oxidizing effect, of storingpolidocanol solution under pressurized oxygen are not fully understood.Therefore, it is preferred at present to have a two canister system inwhich the polidocanol solution is stored under carbon dioxide and/ornitrogen.

In previous versions of the product (as used in Example 1), the gas mixin the polidocanol canister was 25% nitrogen and 75% carbon dioxide. Thenitrogen was present in order to reduce the deleterious effect of thehighly soluble carbon dioxide on the stability of the foam. In order tominimize both the carbon dioxide and the nitrogen content of the foam,this canister was maintained at 0.5 bara. This meant that, when thecanister was connected to the oxygen canister and the final pressureraised to about 3.5 bara, the nitrogen content reduced to around 7%.

It was then realized by the inventors that (1) the canister needed to bemaintained at above atmospheric pressure to avoid the risk ofcontamination and (2) the percentage of nitrogen was too high. A newdesign of can was produced in which the foam generating mesh has smallerapertures—5 micron instead of 20 micron. Although it was previouslythought that differences in size at this level would not have asignificant effect on the foam, it was in fact surprisingly found thatthis reduction in mesh pore size was just sufficient to compensate forthe increased percentage of carbon dioxide which resulted from havingsubstantially pure carbon dioxide in the canister and also frommaintaining it at just over 1 bara instead of 0.5 bara.

Using a polidocanol canister of this design, and an oxygen canister asdescribed above which is pressurized only once, the resulting foam had anitrogen impurity of around 1-2%.

The current procedure is to insert a carbon dioxide line into the opentop of a metal anodized canister for 10 seconds. The line is thenwithdrawn. At this stage not all the air will have been eliminated andit is believed that the nitrogen impurity level is around 5% or 6%. Itis not believed that flushing the canister for a longer period wouldsubstantially change this value for nitrogen gas impurity.

18 ml of 1% polidocanol solution is then introduced into the canister, acarbon dioxide line reintroduced and the canister flushed again for afew seconds.

The head assembly, including dip tube, valve and foam generating meshunit, is then loosely fitted and a filling head brought into engagementaround the top of the canister and valve assembly so as to make agas-tight seal against the canister wall. Connected to the filling headis a line for carbon dioxide. The canister is then brought up to itspressure of approximately 1.2 bara. Nitrogen gas impurity at this stagehas not yet been measured but is expected to be in the region of 0.8%.

The final nitrogen impurity of a foam generated from the chargedpolidocanol canister after it has been connected to the oxygen canisterto bring it up to about 3.5 bara, is given by:(0.8×1.2+0.2×2.3)/3.5=0.4%

EXAMPLE 6

A unit was prepared comprising a housing with ports at each end formedas standard luer connections. Within the housing was an internal pathwaybetween the ports in which pathway four mesh elements were installedsuch that flow between the ports was required to flow through themeshes. The meshes had 5 micron apertures.

8 ml of 1% polidocanol solution was drawn up into a standard 20 mlsyringe and this syringe then fitted to one port of the mesh stack unitdescribed above. A second 20 ml syringe was then taken and 12 ml of airdrawn up into it before fitting it to the other of the two ports on themesh stack unit. The internal volume of the mesh stack unit was measuredand determined to be essentially negligible for these purposes, being0.5 ml or less.

The air and polidocanol solution was then shuttled back and forthbetween the syringes as fast as possible by hand for one minute. Thenumber of passes achieved was 15.

The resulting product was a white liquid of homogeneous appearance withno visible bubbles. A sample of this liquid was analyzed for bubble size(see Example 9 below) and the results tabulated below (Table 2). TABLE 2Number of Bubble diameter (μ) bubbles Cumulative freq. (%) Frequency (%) 0-15 1420 28.4 28.4 15-30 1293 54.3 25.9 30-45 1230 78.9 24.6 45-60 81995.3 16.4 60-75 219 99.7 4.4 75-90 15 100.0 0.3  90-105 0 100.0 0.0105-120 0 100.0 0.0 120-135 0 100.0 0.0 Totals: 4996 100.0

EXAMPLE 7

A similar experiment to Example 6 above was performed with a housingcontaining 4 mesh units each comprising a 5 micron mesh. This time, 10ml of 1% polidocanol solution was drawn up in one 20 ml syringe and 10ml of air drawn up in the other. The air and polidocanol were shuttledback and forth as fast as possible by hand for 2 minutes; 27 passes wereachieved.

The resulting product was a white liquid of homogeneous appearance withno visible bubbles. A sample of this liquid was analyzed for bubble size(see Example 9 below) and the results shown in Table 3 below. TABLE 3Number of Bubble diameter (μ) bubbles Cumulative freq. (%) Frequency (%) 0-15 2387 47.8 47.8 15-30 1293 73.2 25.9 30-45 969 93.1 19.4 45-60 30999.2 6.2 60-75 32 99.9 0.6 75-90 4 100.0 0.1  90-105 2 100.0 0.0 105-1200 100.0 0.0 120-135 0 100.0 0.0 Totals: 4996 100.0

EXAMPLE 8

A similar experiment to Examples 6 and 7 above was performed with ahousing containing 4 mesh units each comprising an 11 micron mesh. 8 mlof 1% polidocanol solution was drawn up in one 20 ml syringe and 12 mlof air drawn up in the other. The air and polidocanol were shuttled backand forth as fast as possible by hand for 1 minute; 25 passes wereachieved.

The resulting product was a white liquid of homogeneous appearance withno visible bubbles. A sample of this liquid was analyzed for bubble size(see example 9 below) and the results shown in Table 4 below. TABLE 4Number of Bubble diameter (μ) bubbles Cumulative freq. (%) Frequency (%) 0-15 620 12.4 12.4 15-30 753 27.5 15.1 30-45 1138 50.3 22.8 45-60 127975.9 25.6 60-75 774 91.4 15.5 75-90 331 98.0 6.6  90-105 85 99.7 1.7105-120 15 100.0 0.3 120-135 1 100.0 0.0 Total: 4996 100.0

EXAMPLE 9 Bubble Sizing Technique

The bubble sizing technique used to measure the bubble size distributionof the foams from Examples 6 to 8 above comprises computer analysis ofthe image of the bubbles though a microscope. A small sample of the foamis deposited on a specially prepared slide which has spacers 37 micronshigh mounted on each side. A further slide is then carefully positionedon top of the sample and spacers, thereby spreading the sample into alayer of 37 micron thickness. A digital image of part of the 37 micronlayer of bubbles is then recorded and processed: the bubbles appear asrings in the image, the ring representing the outermost diameter of thebubble. Each bubble is individually identified and numbered, and itsdiameter calculated. For bubbles over 37 microns in diameter it isassumed that the bubble has been flattened to some degree causing thediameter of the ring in the image to be larger than the diameter of theundeformed bubble. An algorithm for calculating the original diameter ofthe undeformed bubble is applied. For bubbles 37 microns and under, itis assumed that the bubble has floated up against the underside of theupper slide and is undeformed. From visual inspection of the digitalimage, this does not appear to be an unreasonable assumption sinceoverlapping bubble images are either absent completely or are very rare.Nevertheless it is intended to repeat the experiments using a set ofslides with a 10 micron gap and suitably amended software, once thesethings have been developed, so that substantially all the bubbles willbe flattened between the slides.

EXAMPLE 10

Examples 6, 7 and 8 above are repeated using the following method.

Polidocanol solution is drawn up into a 20 ml syringe as described inExamples 6, 7 and 8, ensuring that excess solution is drawn up and thensolution dispensed with the nozzle pointed upwards, until theappropriate volume of polidocanol solution is left. In this way any airvoids in the syringe, particularly in the nozzle, are removed.

The polidocanol-filled syringe is then connected to the mesh unit, theassembly oriented with syringe pointing upwards, and the mesh unitfilled with solution, eliminating all air bubbles.

A line from a cylinder of medical grade oxygen (99.5% purity) isconnected to the luer connector of a 20 ml syringe with the plungerremoved. The oxygen line and syringe barrel and luer connector are thenflushed for 10 seconds with oxygen from the cylinder. The oxygen line isthen removed, keeping the supply of oxygen turned on, and the syringeplunger inserted into the barrel and the plunger depressed. The oxygenline is then re-attached to the syringe luer and the pressure of theoxygen allowed to push the syringe plunger back to fill the syringe withoxygen.

The oxygen syringe is then immediately connected to the mesh unit andthe foam generating procedure described in Examples 6, 7 or 8 carriedout.

EXAMPLE 11

A syringe and mesh unit filled with polidocanol solution as described inExample 10 above are placed in a collapsible “glove box” (a sealablecontainer with integral gloves incorporated into the container wall toallow manipulation by a user of the contents of the container). Afurther, empty syringe is also placed in the glove box. The box is thensealingly connected to vacuum source and thereby collapsed such thatsubstantially all air is removed. The vacuum source is then replaced bya source of 99.995% pure oxygen and the glove box filled with oxygenfrom this source; the oxygen supply is maintained and a small vent isopened in the wall of the glove box opposite the point of entry ofoxygen. The procedure described in Example 10 above for filling theempty syringe with oxygen is then followed, using the 99.995% pureoxygen supply line within the glove box. The procedure described inExamples 6, 7 and 8 is then carried out to generate foam.

EXAMPLE 12

A polidocanol syringe and mesh unit are prepared as in Example 10 above.A syringe is immersed in a tank of water and the plunger removed. Oncethe syringe barrel is completely full of water with no air pockets, astopper is secured over the luer nozzle. The syringe barrel is held withthe nozzle pointing upwards and a line from a 99.9999% pure oxygencylinder is first purged, then introduced into the syringe barrel. Whenall water is replaced by oxygen (taking care that the water in thenozzle is displaced), the plunger is inserted and the syringe removedfrom the water tank. The procedure of Example 10 is then followed toconnect the syringe to the mesh unit and make foam.

As with Example 4 above, this procedure could be refined by storing thewater tank under a continually refreshed atmosphere of 99.9999% pureoxygen for 24 hours prior to filling the syringe.

EXAMPLE 13

In a modification of Examples 10-12, the mesh unit can be replaced witha simple connector or three way valve and in all other respects thetechnique can remain the same, with the possible exception of requiringmore passes to make acceptable foam. The aperture in a standardconnector or three way valve, through which the gas and liquid arepassed, would be about 0.5 mm to 3 mm in its largest dimension. Byrepeatedly passing the liquid and gas through this aperture it is stillpossible to obtain a useful foam, though with bubble sizes considerablylarger than those obtained by the methods of Examples 6 to 12. Thistechnique is commonly known as the “Tessari” technique. The inventorshave experimented with the Tessari technique and found that the size anddistribution of bubbles varies widely according to the ratio of gas toair and also the speed and number of passes of the gas and liquidthrough the aperture. The average bubble size for a Tessari foam hasbeen reported in the literature to be around 300 micron. The best thatthe inventors have managed to achieve using the Tessari technique is afoam with an average bubble size of around 70 micron, though to do thisthe ratio of liquid to gas had to be increased to about 40% liquid, 60%gas.

In this example, the Tessari technique can be adapted to make a foam ofwhatever density and bubble size is desired, within the limitationsdescribed above, but using gas with a very low percentage of nitrogenimpurity.

EXAMPLE 14

A canister was prepared of the type described in WO00/72821-A1 having adip tube and a standard valve assembly provided with a pair of small airinlet apertures, together with a mesh stack unit having a 5 micronaperture size. The size of the apertures in the valve was enlargedslightly compared with the valve arrangement described in WO00/72821-A1(which is designed to produce a foam of density between 1.1 g/ml and 1.6g/ml). The purpose of this modification was to increase the proportionof liquid to gas in the mixture passing through the mash stack.

The canister was filled with 18 ml of 1% polidocanol solution andpressurized with a mixture of oxygen, carbon dioxide and nitrogen. Afoam was then dispensed.

This procedure was repeated for different sizes of valve aperture and anumber of foams produced, all having the appearance of a white liquidand densities in the range 0.3 to 0.5 g/ml. Bubble size analysis wasperformed for each of these foams, which showed the average bubble sizein the region of 50 to 80 micron diameter.

EXAMPLE 15

The above experiment was repeated but with the length and diameter ofthe dip tube adjusted rather than the size of the apertures in the valveunit. It was necessary to increase the volume of liquid in the canisterto ensure that the shortened dip tube reached the liquid level in thecanister. It was possible to produce the same type of foam as describedin Example 6 above.

EXAMPLE 16

The inventors envisage reproducing the above experiments using a pureoxygen or oxygen and carbon dioxide formulation having nitrogen impuritylevels as described above. The same techniques as those described inExamples 4 and 5 may be followed for producing very low levels ofnitrogen impurity.

EXAMPLE 17 Pre-Pressurized Container

A typical apparatus for the generation of therapeutic foam according tothe invention, as disclosed in WO 00/72821-A1, is shown in FIG. 14.

The canister has an aluminum wall (1), the inside surface of which iscoated with an epoxy resin. The bottom of the canister (2) is domedinward. The canister inner chamber (4) is pre-purged with 100% oxygenfor 1 minute, containing 15 ml of a 1% vol/vol polidocanol/20 mmolphosphate buffered saline solution/4% ethanol, then filled with therequired gas mixture.

A standard 1 inch diameter Ecosol™ aerosol valve (5) (Precision Valve,Peterborough, UK) is crimped into the top of the canister after sterilepart filling with the solution and may be activated by depressing anactuator cap (6) to release content via an outlet nozzle (13) sized toengage a Luer fitting of a syringe or multi-way connector (not shown). Afurther connector (7) locates on the bottom of the standard valve andmounts four Nylon 66 meshes held in high density polyethylene (HDPE)rings (8), all within an open-ended polypropylene casing. These mesheshave diameter of 6 mm and have a 14% open area made up of 20 μm pores,with the meshes spaced 3.5 mm apart.

A further connector (9) locates on the bottom of the connector holdingthe meshes and receives a housing (10) which mounts the dip tube (12)and includes gas receiving holes (11 a, 11 b) which admit gas fromchamber (4) into the flow of liquid which rises up the dip-tube onoperation of the actuator (6). These are conveniently defined by anEcosol™ device provided by Precision Valve, Peterborough, UK, providedwith an insert. Holes (11 a, 11 b) have cross-sectional area such thatthe sum total ratio of this to the cross-sectional area of the liquidcontrol orifice at the base of the valve housing (at the top of thedip-tube) is controlled to provide the required gas/liquid ratio.

EXAMPLE 18 Container with Engaging Means and Mesh Stack Shuttle

A device comprising a container provided with engaging means and a meshstack shuttle according to the invention, as disclosed in WO02/41872-A1, is shown in FIG. 15. The device comprises a low pressurecontainer (1) for an aqueous sclerosant liquid and an unreactive gasatmosphere, a container (2) for a physiologically acceptableblood-dispersible gas and an engaging means comprising a connector (3).

The container (2) for a physiologically acceptable blood-dispersible gasis charged at 5.8 bar absolute pressure with the required gas mixture,whereas the container (1) is charged with an inert gas. Container (2) isused to pressurize container (1) at the point of use to approx 3.5 barabsolute and is then discarded, just before the foam is required. Thetwo containers will thus be referred to hereinafter as the PD[polidocanol] can (1) and the O2 can (2), and the term “bi-can” will beused to refer to the concept of two containers.

Each of the cans (1, 2) is provided with a snap-fit mounting (4, 5).These may be made as identical mouldings. The snap-fit parts (4, 5)engage the crimped-on mounting cup (6, 7) of each can (1, 2) with highfrictional force. The connector is made in two halves (8, 9), and thehigh frictional force allows the user to grip the two connected cans (1,2) and rotate the connector halves (8, 9) relative to each other withoutslippage between connector (3) and cans. Each of these can mountings (6,7) has snap-fit holes (10, 11) for engaging mating prongs (12, 13) whichare on the appropriate surfaces of the two halves (8, 9) of theconnector.

The connector (3) is an assembly comprising a number of injectionmouldings. The two halves (8, 9) of the connector are in the form of camtrack sleeves which fit together as two concentric tubes. These tubesare linked by proud pins (14) on one half that engage sunken cam tracks(15) on the other half. The cam tracks have three detented stoppositions. The first of these detents is the stop position for storage.An extra security on this detent is given by placing a removable collar(16) in a gap between the end of one sleeve and the other. Until thiscollar (16) is removed it is not possible to rotate the sleeves past thefirst detent position. This ensures against accidental actuation of theconnector.

The cam track sleeves (8, 9) are injection moulded from ABS as separateitems, and are later assembled so that they engage one another on thefirst stop of the detented cam track. The assembled sleeves aresnap-fitted as a unit onto the O2 can (2) mounting plate (5) via fourlocating prongs. The security collar is added at this point to make anO2 can subassembly.

The connector (3) includes in its interior a series of foaming elementscomprising a mesh stack shuttle (17) on the connector half (8) adjacentto the PD can (1). The mesh stack shuttle (17) is comprised of fourinjection moulded disk filters with mesh hole size of 20 μm and an openarea of approx. 14%, and two end fittings, suitable for leak-freeconnection to the two canisters. These elements are pre-assembled andused as an insert in a further injection moulding operation that encasesthem in an overmoulding (18) that provides a gas-tight seal around themeshes, and defines the outer surfaces of the mesh stack shuttle. Theend fittings of the stack (17) are designed to give gas-tight faceand/or rim seals against the stem valves (19, 20) of the two cans (1, 2)to ensure sterility of gas transfer between the two cans.

The mesh stack shuttle (17) is assembled onto the PD can valve (19) bypush-fitting the components together in a aseptic environment.

The PD can (1) and attached shuttle (17) are offered up to the connector(3) and the attached O2 can (2), and a sliding fit made to allowsnap-fitting of the four locating prongs (12) on the PD can side of theconnector (3) into the mating holes (10) in the mounting plate (4) onthe PD can (1). This completes the assembly of the system. In thisstate, there is around 2 mm of clearance between the stem valve (20) ofthe O2 can (2) and the point at which it will form a seal against afemale Luer outlet from the stack.

When the security collar (16) is removed, it is possible to grasp thetwo cans (1, 2) and rotate one half of the connector (3) against theother half to engage and open the O2 can valve (20).

As the rotation of the connector (3) continues to its second detentposition, the PD can valve (19) opens fully. The gas flow from the O2can (2) is restricted by a small outlet hole (21) in the stem valve(20). It takes about 45 seconds at the second detent position for thegas pressure to (almost) equilibrate between the two cans to a level of3.45 bar±0.15 bar.

After the 45 second wait at the second detent position, the connector(3) is rotated further to the third detent position by the user. At thisposition, the two cans (1, 2) can be separated, leaving the PD can (1)with half (8) of the connector and the shuttle assembly (17) captivebetween the connector and the PD can. The O2 can (2) is discarded atthis point.

A standard 1 inch diameter aerosol valve (19) (Precision Valve,Peterborough, UK) is crimped into the top of the PD can (1) before orafter sterile filling with the solution and may be activated bydepressing the mesh stack shuttle (17), which functions as an aerosolvalve actuator mechanism, to release the contents via an outlet nozzle(22) sized to engage a Luer fitting of a syringe or multi-way connector(not shown).

EXAMPLE 19 Study to Assess the Effect on Physical Properties of Foamfrom Changes to the Mesh Material in the Mesh Stack

This study outlines the effect on foam properties of changing theshuttle mesh pore size from 20 microns to 5 microns, in combination withchanges to the gas pressure and gas composition in the canister. Thestudy dates from before the inventors' realization that a nitrogenconcentration of 0.8 or below was desirable. Its main purpose was totest whether use of a 5 micron instead of a 20 micron mesh willcompensate for eliminating the 25% nitrogen which was previouslydeliberately incorporated into the polidocanol canister. The “100%”carbon dioxide and “100%” oxygen referred to in this and the followingexamples will in fact incorporate levels of nitrogen impurity and thefinal dual canister product discussed in these examples will probablyproduce as foam of about 1-2% nitrogen impurity.

Two different gas compositions were used. In one, the canistercontaining the 1% polidocanol solution and a 75%/25% atmosphere ofCO2/N2 is evacuated to 0.5 bar absolute pressure, whilst the othercanister is pressurised to 5.9 bar absolute with oxygen. In the other,the canister containing the 1% polidocanol solution is pressurised to1.2±0.1 bar absolute with 100% CO2, whilst the other canister ispressurised to 5.8±0.1 bar absolute with oxygen.

The objective of the study is to examine and compare results obtainedusing 5 micron and 20 micron shuttle meshes, for PD canister pressuresof 0.5 bar absolute with the current gas atmosphere and for 1.2 barabsolute PD canister pressures with a 100% CO2 as the filling gas.

Materials and Methods:

All sample preparation was performed in a laminar flow booth keepingexposure times to atmosphere to a minimum.

Shuttle units containing a stack of 4 nylon 6/6 woven meshes of 6 mmdiameter in a class 100K cleanroom moulding facility were used. Theydiffer in the following aspects shown in Table 3 below. TABLE 5 Physicalcharacteristics of the 20 μm and 5 μm meshes compared Open MeshThickness Pore size Area (% area of Thread diameter Type (μm) (μm)pores) (μm)  5 μm 100 5 1 37 20 μm 55 20 14 34

Bioreliance Ltd, Stirling, Scotland, U.K., made the 1% polidocanolsolution for the study under controlled conditions to the formula inTable 4. TABLE 6 Composition of the 1% polidocanol solution QuantitiesMaterial % w/w per 1000 g Polidocanol 1.000  10.00 g Ethanol 96% EP4.200  42.00 g Disodium Hydrogen Phosphate 0.240   2.40 g Dihydrate. EPPotassium Di-hydrogen Phosphate. EP 0.085   0.85 g 0.1 M SodiumHydroxide Solution [used q.s. q.s. for adjustment of pH: 7.2-7.5] 0.1 MHydrochloric Acid q.s. q.s. Water for injection. EP [used to adjust toapprox. 94.475 q.s. to approx. 944.75 g q.s. final weight] 100.00% to1000.00 g TOTAL: 100.00% 1000.00 g

The polidocanol solution was sterile filtered using a 0.2-micron filterbefore filling into clean glass screw top bottles.

Bi-can assemblies were prepared for testing to the specifications of gasmix and pressure in the polidocanol canister detailed in Table 5. TABLE7 Summary of PD canister preparation for each treatment group CanisterSample Gas Gas Pressure Mesh Pore Size Label Type Composition (barabsolute) (μm) C Control 1 75% CO₂/25% 0.5 20 N₂ D Test 1 75% CO₂/25%0.5 5 N₂ A Control 2 100% CO₂ 1.2 20 B Test 2 100% CO₂ 1.2 5

The order of testing of the experimental series was important, in thatchanges in ambient laboratory temperature affect the half separationtime results. Experiments progressed cyclically through the sample typesrather than test all of one sample type, followed by all of anothersample type. This minimized the effect of any drift in laboratorytemperature throughout the experiments. The laboratory temperature wasmaintained as close to 20° C. as possible.

It was also essential that the temperature of the half separation timeapparatus be allowed to fully equilibrate to ambient room temperaturefollowing cleaning and drying steps between successive experimentalmeasurements.

Summary of Tests:

The tests and specifications performed on the bi-can units in this studyare summarized in Table 6. TABLE 8 Summary of tests and specificationsTEST SPECIFICATION 1 Appearance of Device No corrosion of canisters orvalves. Free from signs of leakage and external damage 2 Gas Pressure1.10 to 1.30 bar absolute for Type 2 samples Polidocanol Canister 0.4 to0.6 bar absolute for Type 1 samples Oxygen Canister 4.90 to 5.9 barabsolute 3. Appearance of Foam Upon actuation, a white foam is produced.After the foam has settled, a clear and colourless liquid is observed.4. pH of Solution 6.6 to 7.5 (collapsed foam) 5 Foam density 0.10 to0.16 g/ml. 6 Foam Half Separation 150 to 240 seconds Time 7 Bubble Size(Diameter Distribution) <30 μm ≦20.0% 30 μm to 280 μm ≧75.0% 281 μm to500 μm ≦5.0% >500 μm None 8 Particulates (Visible) Complies with Ph.Eur. and Sub-Visible) 9 Particulates (Sub- The collapsed foam containsnot more than 1000 Visible) particles per ml ≧10 μm and not more than100 particles ≧25 μm per ml. 10 Polidocanol GC pattern and retentiontimes to be equivalent to identification by GC reference preparationmethod 11 Polidocanol Assay 0.90 to 1.10% w/w 12 Related Substances Nosingle identified impurity >0.20% area. No single unidentifiedimpurity >0.10% area. Total impurities ≦4.0% area

Results:

Results of the tests described in Table 6 on bi-cans prepared asdescribed in Table 5 are summarized in the following paragraphs.

Appear of Device and Foam

In all cases the appearance of the devices conformed to specification inthat the device showed no corrosion of canisters or valves and were freefrom signs of leakage and external damage. Upon actuation of the chargedPD canister a white foam was produced. After the foam had settled, aclear and colorless liquid was observed.

Density, Half Separation Time and pH

Foam from all devices conformed to density and half separation timespecification. However, one unexpectedly low result was obtained (C1canister 1) but an additional two devices were tested which behaved asexpected. In spite of the low result, the average conformed tospecification. In general, foam generated via the 5 □m shuttles hadlonger half separation times. Results are summarized in Table 7.

The average pH of the foam generated conformed to specification.However, foam produced from the 100% CO2 canister were close to thelower limit of detection of the specification and in one instance (C2canister 4) it was just below specification. Results summarized in Table7.

The gas pressure in the oxygen cans and the polidocanol cans conformedto specification in all cases. In one instance (C1 canister 6) aslightly lower oxygen canister pressure than expected was recorded.Results are summarized here in Table 7. TABLE 9 Table summarising thefoam density, half separation time, pH and canister gas pressures Gaspressure density half life (bars abs) Test Condition (g/cm³) (sec) pHOxygen PD Specification 0.10-0.16 150-240 6.6-7.5 4.9-5.9 0.4-0.6 100%CO₂, 1.2 Bar, 20 μm mesh Canister A1 0.12 164 6.7 5.6 1.1 Canister A20.13 150 6.7 5.5 1.1 Canister A3 0.13 153 6.6 5.8 1.1 Canister A4 0.15154 6.5 5.5 1.1 Canister A5 0.13 154 6.7 5.6 1.1 Canister A6 0.15 1546.5 5.6 1.1 Average 0.13 155 6.6 5.6 1.1 100% CO₂, 1.2 Bar, 5 μm meshCanister B1 0.12 182 6.6 5.4 1.1 Canister B2 0.12 169 6.7 5.6 1.1Canister B3 0.14 162 6.6 5.4 1.1 Canister B4 0.1 173 6.7 5.7 1.1Canister B5 0.12 168 6.6 5.6 1.1 Canister B6 0.15 161 6.5 5.4 1.1Average 0.13 169 6.6 5.5 1.1 75% CO₂/25% N₂, 0.5 Bar, 20 μm meshCanister C1 0.14  157# 6.9 5.4 0.6 Canister C2 0.15 182 6.9 5.5 0.6Canister C3 0.13 193 6.9 5.4 0.6 Canister C4 0.15 183 6.9 5.7 0.6Canister C5 0.15 192 6.8 5.6 0.5 Canister C6 0.15 191 6.9 5.0 0.6Canister C11 0.14 189 7.0 5.7 0.6 Canister C12 0.13 179 7.0 5.4 0.6Average 0.14 183 6.9 5.5 0.6 75% CO₂/25% N₂, 0.5 Bar, 5 μm mesh CanisterD1 0.15 203 6.9 5.4 0.6 Canister D2 0.12 209 7.0 5.6 0.6 Canister D30.16 198 6.8 5.6 0.6 Canister D4 0.12 205 6.9 5.7 0.6 Canister D5 0.12208 6.9 5.4 0.6 Canister D6 0.15 205 6.9 5.6 0.6 Average 0.14 205 6.95.6 0.6

Bubble Size Distribution:

The average bubble size for all conditions was within specification withthe exception of control 1 (C) where the >500 □m which averaged at oneoversized bubble. Results are summarized here in Table 8. TABLE 10 Tableto summarise the bubble size distribution of foam generated BubbleDiameters (μm) <30 30-280 281-500 >500 Specification <=20% >=80% <=5%None 100% CO_(2,) 1.2 Bar, 20 μm mesh Canister A1  8.2% 89.5% 2.3% 0Canister A2  8.1% 89.7% 2.2% 0 Canister A3  7.9% 85.3% 6.8% 0 CanisterA4  9.0% 88.3% 2.6% 1 Canister A5  7.9% 90.7% 1.5% 0 Canister A6 11.0%88.1% 0.9% 0 Average  8.7% 88.6% 2.7% 0 100% CO₂, 1.2 Bar, 5 μm meshCanister B1  7.8% 91.8% 0.4% 0 Canister B2  5.5% 94.2% 0.3% 0 CanisterB3  8.6% 90.7% 0.7% 0 Canister B4  8.8% 91.1% 0.2% 0 Canister B5  7.7%92.2% 0.0% 0 Canister B6  8.2% 91.3% 0.5% 0 Average  7.8% 91.9% 0.4% 075% CO₂/25% N₂, 0.5 Bar, 20 μm mesh Canister C1  8.9% 87.2% 3.9% 0Canister C2 10.0% 89.3% 0.6% 0 Canister C3  8.9% 86.5% 4.5% 1 CanisterC4  9.7% 87.7% 2.5% 4 Canister C5 10.7% 87.9% 1.5% 0 Canister C6 10.1%88.0% 1.9% 0 Canister C11  9.6% 89.5% 1.0% 0 Canister C12 11.0% 87.6%1.4% 0 Average  9.7% 88.1% 2.5% 1.0 75% CO₂/25% N₂, 0.5 Bar, 5 μm meshCanister D1  7.8% 92.0% 0.2% 0 Canister D2  8.1% 91.4% 0.6% 0 CanisterD3 10.9% 89.0% 0.1% 0 Canister D4  8.5% 91.2% 0.2% 0 Canister D5  8.8%91.1% 0.1% 0 Canister D6 10.2% 89.8% 0.0% 0 Average  9.0% 90.7% 0.2% 0#Value from Control 1, canister 1 are not included in the average

Particulates (Sub Visible)

The collapsed foam from all canisters complied to specification forparticulates, in so far as there were no more than 1,000 particles/ml≧10μm and no more than 100 particles/ml≧25 μm. Those which had 100% CO2 gasmixture gave the lowest numbers of particles overall. There were novisible particles seen in the collapsed foam. The results are summarizedhere in Table 7.

The appearance of foam from each device conformed to specification. Theappearance of all canisters conformed to specification. TABLE 11Sub-visible particulates as per in house method MS14 Counts per mlCounts per container (18 ml) Device No ≧10 μm ≧10-25 μm ≧25 μm ≧10 μm≧10-25 μm ≧25 μm Result Ref A Can 7 281.6 271.4 10.2 5,069 4,885 184Complies Ref A Can 8 235.3 227.9 7.4 4,235 4,102 133 Complies Ref B Can7 112.8 109.8 3 2,030 1,976 54 Complies Ref B Can 8 123.1 116.3 6.82,216 2,093 122 Complies Ref C Can 7 386.1 370.2 15.9 6,950 6,664 286Complies Ref C Can 8 369.5 350.6 18.9 6,651 6,311 340 Complies Ref D Can7 130.2 123.5 6.7 2,344 2,223 121 Complies Ref D Can 8 152.1 141.4 10.72,738 2,545 193 Complies

Polidocanol Identification, Assay and Related Substances

No significant differences were observed between the results of theControl and Test preparations. All samples met all specifications forrelated substances, assay value and identity.

Analysis of the samples using the 25 m column was undertaken, but nosignificant peaks were observed relating to Nylon 6,6 interactions inthese samples.

EXAMPLE 20 Further Study to Assess the Effect on Physical Properties ofFoam from Changes to the Mesh Material in the Mesh Stack

The study of Example 9 was repeated using a device in which the shuttlemesh pore size was 20 microns, 11 microns and 5 microns, in combinationwith changes to the gas pressure and gas composition in the canister.Bi-can assemblies were prepared for testing to the specifications of gasmix and pressure in the polidocanol canister detailed in Table 9. TABLE12 Summary of PD canister preparation for each treatment group SampleGas Pressure Mesh Pore Size Type Gas Composition (bar absolute) (μm)Control 1  75% CO₂/25% N₂ 0.5 20 Control 2 100% CO₂ 1.2 20 Test 2 100%CO₂ 1.2 5 Test 3 100% CO₂ 1.2 11

Various batches of the foam resulting from the test in which the shuttlemesh pore size was 11 microns had the following characteristics: TABLE13 (a). Bubble Diameter (micrometers) <=30 >30 − 280 >280 − 500 >5009.2% 90.2% 0.6% 0.0% 11.8% 88.2% 0.0% 0.0% 10.6% 89.4% 0.0% 0.0% 10.2%89.8% 0.0% 0.0% 10.6% 89.1% 0.3% 0.0% 10.5% 89.4% 0.1% 0.0% (b). BubbleDiameter (micrometers) excluding below 30 μm <30 − 130 >30 − 280 >280 −500 >500 59.1% 99.4% 0.6% 0.0% 71.2% 100.0% 0.0% 0.0% 75.3% 100.0% 0.0%0.0% 67.3% 100.0% 0.0% 0.0% 66.4% 99.7% 0.3% 0.0% 73.6% 99.9% 0.1% 0.0%

TABLE 14 Density and Half Life Density (g/cm3) Half Life (Min) 0.12 180sec 0.14 171 sec 0.14 175 sec 0.12 175 sec 0.13 177 sec 0.15 177 sec

EXAMPLE 21

Experiments were conducted to compare the physical properties ofsclerosing foam made by the methods of Cabrera, using a range of CO2/O2gas mixtures as the ambient atmosphere in which a small brush is rotatedat high speed to whip polidocanol (PD) solution into a foam, asdisclosed in EP 0656203.

All sample preparation was performed under controlled laboratoryconditions at temperatures within the range 18-22 degrees C., usingpolidocanol solution obtained from Kreussler 1% Aethoxysclerol. Thecontainer was a 100 ml beaker. The beaker and the 10 ml of solution wasplaced in a small glass aquarium tank which was modified to allow theinternal space to be sealed from atmosphere, then flushed and floodedwith the test gas mix.

During the experiments, a small ingress of the test gas mix was presentto ensure that atmospheric nitrogen and oxygen cannot enter the glasstank and change the known gas mix. A flexible drive shaft was attachedto the micromotor to allow the micromotor to stay outside of the glasstank, whilst driving the brush inside the glass tank at the requiredspeed. Where the flexible drive shaft entered the glass tank, it wassealed to avoid leaks from atmosphere.

The flushing of the glass tank was performed for 30 seconds with the gasmix supplied at 0.2 bar above atmospheric pressure to the glass tank.After the 30 second flush, the regulator was turned down to allow atrickle of ingressing gas for the rest of the experiment. The speed ofrotation and duration of whipping was fixed at 11500 rpm and 90 seconds.

The results in Table 15 show the density and half life of foams madewith 100% CO2, 100% O2, 75% CO2/25%O2 and air. For each gas, foams weremade with plain polidocanol, polidocanol and 5% glycerol, polidocanoland 25% glycerol and polidocanol and 40% glycerol. Two runs are reported(1 and 2) for each foam. The results show that higher percentages ofglycerol enable one to make a CO2 foam with adequate density and halflife. TABLE 15 (a) Air Density and Half Separation Time Density (g/ml)Half Life (Sec) Plain PD air 1 0.16 173 Plain PD air 2 0.17 170 5%glycerol 1 0.20 188 5% glycerol 2 0.20 195 25% glycerol 1 0.30 539 25%glycerol 2 0.27 535 40% glycerol 1 0.44 459 40% glycerol 2 0.45 575 (b)100% O2 Density and Half Separation Time Density (g/ml) Half Life (Sec)Plain PD O2 1 0.18 122 Plain PD O2 2 0.17 120 O25GA 0.18 144 O25GB 0.18140 O225ga 0.30 343 O225gb 0.34 429 O240ga 0.47 432 O240gb 0.44 525 (c)75% CO2/25% O2 Density and Half Separation Time Density (g/ml) Half Life(sec) 2575 plain PD 1 0.20 72 2575 plain PD 2 0.18 78 2575 5% G A 0.1681 2576 5% G B 0.19 82 2575 25% G A 0.33 216 2576 25% G B 0.29 229 257540% G A 0.46 399 2576 40% G B 0.47 410 (d) 100& CO2 Density and HalfSeparation Time Density (g/ml) Half Life (Min) Plain PD CO2 1 0.19 55Plain PD CO2 2 0.19 71 CO25GA 0.24 57 CO25GB 0.20 66 CO225ga 0.29 187CO225gb 0.33 239 co240ga 0.48 227 co240gb 0.51 273

EXAMPLE 22 Polidocanol, Glycerol and CO2 Foams

Foams were made with polidocanol, glycerol and CO2 using varioustechniques. The technique used to make the foam plays an important rolein the half life and density of the resulting foam.

Double Syringe Technique

500 ml of a buffered solution of 1% polidocanol and 30% glycerol wasmade up using the following procedure.

100% polidocanol (pd)—a waxy solid—was melted by placing in a bath ofwarm water

100 ml distilled water was weighed out in a 1000 ml beaker

0.425 g potassium dihydrogen phosphate was added as a stabilizer

5 g of the liquefied pd was weighed out

21 g of 96% ethanol was weighed out

The ethanol and pd were mixed, then added to distilled water

150 g glycerol was added

Water was added to the 425 ml mark

pH was adjusted by adding 0.1M sodium hydroxide to between 7.34 and 7.38pH.

Distilled water was added to make up to 500 g on scale

The solution was filtered through a 0.25 micron filter.

The same procedure was followed, with an increased amount of glycerol,to make the 40% glycerol solution.

Into a 50 ml glass syringe was drawn 10 ml of the pd/glycerol solution.The nozzle of another 50 ml glass syringe was connected to a line from acylinder of carbon dioxide (B.O.C. “C.P grade” having a purity level of99.995%). The syringe was filled with carbon dioxide and then removedfrom the line, the plunger depressed and the syringe then re-filled tothe 50 ml graduation on the syringe barrel and then detached from theline. A connector having a female luer at each end and a through bore ofdiameter approximately 1 mm was then connected to the line and flushedthrough. The two syringes were then each connected to the connectordevice.

The carbon dioxide and pd/glycerol solution were then manually pumpedback and forth between the two syringes as fast as possible for inexcess of 30 cycles. A foam formed in the syringes during this process.After the final cycle, the foam was quickly transferred to half-life anddensity measuring apparatus and the half life and density of the foamdetermined.

The procedure was carried out for a buffered solution of 1% polidocanoland 30% glycerol and for a buffered solution of 1% polidocanol and 40%glycerol.

In each case the resulting foam was observed to be somewhat runny,though not like a liquid. It would form very flat, gently rounded “blob”on a surface which decayed and ran away as liquid within five seconds.

Double Syringe and Mesh Technique

The procedure outline above for the double syringe technique wasfollowed, with the following variations.

Instead of using a connector with a 1 mm bore, a so called “mesh stack”device was prepared having a flow path which incorporated a series offour mesh elements. Each mesh element measured about 2-3 mm in diameterand had pores with diameter 5 micron. At each end of the device was aluer connection.

The syringes were again cycled as fast as possible but this wasconsiderably slower than was possible with the simple connector having a1 mm bore. After 10 cycles the pumping of the syringes was stopped sinceno further changes in the foam could be observed. Two operators werenecessary to perform this cycling, each operator depressing the plungeron a respective syringe.

The procedure was carried out for a buffered solution of 1% polidocanoland 30% glycerol and for a buffered solution of 1% polidocanol and 40%glycerol.

The appearance of the foams made with the double syringe and mesh stacktechnique was quite similar to those produced with the double syringestyle technique; however the “blobs” were less flat and took somewhatlonger to decay.

Canister Technique

Pressurized canisters with a capacity of approximately 100 ml were madeup with about 20 ml of buffered polidocanol/glycerol solution. Thecanisters were then pressurized with substantially pure carbon dioxideto a pressure of 3.5 bar absolute.

The canisters are each fitted with a valve, with a dip tube extendingfrom the valve to the base of the canister. On each side of the valveare apertures which draw in gas as liquid passes up the dip tube underpressure. Above the valve, each canister is fitted with a mesh stackunit as described above.

To dispense foam, the canister valve is opened. The first portion offoam is discarded and then foam is dispensed directly into the half lifeand density measurement apparatus.

The procedure was carried out with canisters containing a bufferedsolution of 1% polidocanol and 30% glycerol and with canisterscontaining a buffered solution of 1% polidocanol and 40% glycerol.

The foam produced by the 30% glycerol solution was relatively stiff andformed a compact, rounded blob on a surface. The blob could be seen tostart decaying within a few seconds, but remained as a blob rather thana liquid puddle for much longer. Observations were not recorded for the40% glycerol.

Results

Double Syringe Foam

1) (100% CO2, 1% polidocanol, 30% glycerol)

-   -   Density=0.231; Half life=99 secs

2) (100% CO2, 1% polidocanol, 40% glycerol)

-   -   Unable to make sufficient amount of foam

Double Syringe and Mesh Technique

1) (100% CO2, 1% polidocanol, 30% glycerol)

-   -   Density=0.174; Half life=155 secs

2) (100% CO2, 1% polidocanol, 40% glycerol)

-   -   Density=0.186; Half life=166 secs

Canister

1) (100% CO2, 1% polidocanol, 30% glycerol)

-   -   Density=0.094; Half life=121 secs

2) (100% CO2, 1% polidocanol, 30% glycerol)

-   -   Density=0.124; Half life=166 secs

3) (100% CO2, 1% polidocanol, 30% glycerol)

-   -   Density=0.124; Half life=108 secs

EXAMPLE 23 Polidocanol, Glycerol and CO2 Foams

The effects of different viscosity enhancing agents (glycerol, PVP andethanol) on the viscosity of the liquid phase before producing a foamwere examined. Viscosity was determined at 23 oC using the Brookfielddevice described above.

The effects of additional components on the density and half life of CO2foams made using the methods of Cabrera was also studied. Foams wereprepared using the polidocanol (PD) and different percentages ofviscosity enhancing agents (wt/wt) and the Cabrera method describedabove. The half life and density of the resulting foam was determined asdescribed above. Similar experiments can be used to determine if aparticular combination of viscosity enhancing agent, sclerosing agent,and gas provide a foam with a suitable half-life and density. Foams werealso produced using a canister as described above and the results arepresented in Table 16. TABLE 16 Canister CO2/glycerol resultsComposition Viscosity (all compositions Half life Average Average ofLiquid are 100% CO2 & Density (sec- Density Half life Component 1%polidocanol) (g/ml) onds) (g/ml) (seconds) (cP)  5% glycerol 0.105 760.112 63 1.5  5% glycerol 0.109 58  5% glycerol 0.111 60  5% glycerol0.117 59  5% glycerol 0.121 61 10% glycerol 0.112 78 0.117 76 1.6 10%glycerol 0.115 75 10% glycerol 0.118 78 10% glycerol 0.124 73 20%glycerol 0.113 92 0.115 96 2.2 20% glycerol 0.113 99 20% glycerol 0.113104 20% glycerol 0.120 95 20% glycerol 0.114 90 25% glycerol 0.105 1110.109 111 2.6 25% glycerol 0.106 109 25% glycerol 0.108 109 25% glycerol0.109 118 25% glycerol 0.115 106 30% glycerol 0.094 121 0.114 132 — 30%glycerol 0.124 166 30% glycerol 0.124 108 40% glycerol 0.083 172 0.118173 — 40% glycerol 0.133 174 40% glycerol 0.137 174  1% PVP C30 0.091 730.107 67 1.6  1% PVP C30 0.107 62  1% PVP C30 0.111 69  1% PVP C30 0.11964  2% PVP C30 0.102 70 0.107 68 2.0  2% PVP C30 0.105 69  2% PVP C300.106 69  2% PVP C30 0.114 63  1% PVP K90 0.068 142 0.073 135 5.0  1%PVP K90 0.071 118  1% PVP K90 0.072 129  1% PVP K90 0.074 159  1% PVPK90 0.078 129

1. A device for generating and dispensing a foam for therapeutic usecomprises: (a) a housing; (b) the housing comprising a first chamber ofadjustable volume comprising gas at substantially atmospheric pressureor greater; (c) the housing further comprising a second chamber ofadjustable volume comprising a solution comprising at least onesclerosant agent; (d) an outlet for dispensing the gas and the solutionin the form of a foam and a flow path communicating between the outletand the first and second chambers; (e) the flow path comprising a regionin which mixing of the gas and the solution takes place; (f) a foamingunit located downstream of the mixing region, the foaming unitcomprising holes with a dimension transverse to the flow direction ofbetween 0.1 and 100 micron.
 2. The device of claim 1 wherein the gas isat least 70% by volume oxygen.
 3. The device of claim 1, wherein the gasis at least 90% oxygen.
 4. The device of claim 1, wherein the gas is atleast 99% oxygen.
 5. The device of claim 1, wherein the gas issubstantially 100% oxygen.
 6. The device of claim 1 wherein the gas isat least 70% by volume carbon dioxide.
 7. The device of claim 1, whereinthe gas is at least 90% carbon dioxide.
 8. The device of claim 1,wherein the gas is at least 99% carbon dioxide.
 9. The device of claim1, wherein the gas is substantially 100% carbon dioxide.
 10. The deviceof claim 1, wherein a source of motive power is provided to adjust thevolume of one or both of the said chambers.
 11. The device of claim 1,wherein the housing is a syringe having twin plungers.
 12. The device ofclaim 1, wherein the cross sectional area of the first and secondchambers are in a ratio of between 20:1 and 2:1.
 13. The device of claim12, wherein the cross sectional area of the first and second chambersare in a ratio of between 20:1 and 2:1.
 14. The device of claim 1,wherein the housing is a flexible bag.
 15. The device of claim 1,wherein the gas is chosen from oxygen, carbon dioxide and mixturesthereof.
 16. The device of claim 1, wherein the solution furthercomprises at least one viscosity enhancing agent.
 17. The device ofclaim 16, wherein the at least one viscosity enhancing agent is presentin the amount of 20% vol/vol.
 18. The device of claim 17, wherein the atleast one viscosity enhancing agent is chosen from glycerol and PVP. 19.The device of claim 18, wherein the at least one viscosity enhancingagent is chosen from glycerol.
 20. The device of claim 1, wherein the atleast one sclerosing agent is chosen from polidocanol, glycerol andsodium tetradecyl sulphate.
 21. The device of claim 1, wherein the atleast one sclerosing agent is polidocanol.
 22. The device of claim 1,wherein the polidocanol is present in a concentration ranging from 0.5to 4% vol/vol in the solution.
 23. The device of claim 1, wherein thefoam has a density less than 0.25 g/cm and half life of greater than 100secs.